Method for tuning characteristics of a polyamide nanofiber nonwoven

ABSTRACT

A method for tuning characteristics of a polyamide nanofiber nonwoven comprising the step of targeting a specific average nanofiber diameter and/or a specific relative viscosity for the polyamide nanofiber nonwoven. The specific average nanofiber diameter is within a range from 100 nm to 1000 nm and/or the specific relative viscosity is within a range from 5 to 75, e.g., from 15 to 50. The process further comprises the steps of extruding a polyamide composition having a moisture content with a pressurized gas through a fiber forming channel having a channel temperature to form the polyamide nanofiber nonwoven having the target average nanofiber diameter and/or relative viscosity and controlling the moisture content, the pressure of pressurized gas, and/or the channel temperature based on the specific average nanofiber diameter and/or the specific relative viscosity.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application No.62/682,465, entitled “Tunable Nanofiber Nonwoven Products,” filed Jun.8, 2018, the disclosure of which is incorporated herein by reference inits entirety.

TECHNICAL FIELD

The present invention relates to tunable processes for making polyamidenanofiber nonwoven products, which are useful for air and liquidfiltration, breathable fabrics for apparel, acoustics, composites andpackaging, as well as other applications.

BACKGROUND

Polymer membranes, including nanofiber and microfiber nonwovens areknown in the art and are used for a variety of purposes, including inconnection with filtration media and apparel. Known techniques forforming finely porous polymer structures include xerogel and aerogelmembrane formation, electrospinning, melt-blowing, as well ascentrifugal-spinning with a rotating spinneret and two-phase polymerextrusion through a thin channel using a propellant gas. Thesetechniques are either expensive or do not form nanofibers, e.g.,polyamide nanofibers, with acceptable fiber diameter distributions.Electrospinning, for example, is a relatively expensive process andcurrent melt-blowing techniques, while less expensive, do not attain thenanofiber size that electrospinning can attain.

US Pub. No. 2014/0097558 relates generally to methods of manufacturing afiltration media, such as a personal protection equipment mask orrespirator, which incorporates an electrospinning process to formnanofibers onto a convex mold, which may, for example, be in the shapeof a human face. See, also, US Pub. No. 2015/0145175 A1.

WO 2014/074818 discloses nanofibrous meshes and xerogels used forselectively filtering target compounds or elements from a liquid. Alsodescribed are methods for forming nanofibrous meshes and xerogels,methods for treating a liquid using nanofibrous meshes and xerogels, andmethods for analyzing a target compound or element using nanofibrousmeshes and xerogels. The nanofibers are comprised of polysiloxanes.

WO 2015/003170 relates to nonwoven textiles consisting of webs ofsuperfine fibers, i.e., fibers with diameters in nanoscale ormicronscale ranges, for use in articles that have, for example apredetermined degree of waterproofness with breathability, orwindproofness with breathability. The fibers may comprisepolyurethane-based material or polytetrafluoroethylene.

WO 2015/153477 relates to a fiber construct suitable for use as a fillmaterial for insulation or padding, comprising: a primary fiberstructure comprising a predetermined length of fiber; a secondary fiberstructure, the secondary fiber structure comprising a plurality ofrelatively short loops spaced along a length of the primary fiber. Amongthe techniques enumerated for forming the fiber structures includeelectrospinning, melt-blowing, melt-spinning and centrifugal-spinning.The products are reported to mimic goose-down, with fill power in therange of 550 to 900.

Despite the variety of techniques and materials proposed, the desirableability to adjust, control, or otherwise set properties andcharacteristics of the end products has not been sufficientlycontemplated. Further, conventional products and processes leave much tobe desired in terms of manufacturing costs, processability, and productproperties.

SUMMARY OF INVENTION

In one embodiment, the present disclosure is directed to a method fortuning characteristics of a polyamide nanofiber nonwoven comprising thesteps of targeting a specific average nanofiber diameter and/or aspecific relative viscosity for the polyamide nanofiber nonwoven,wherein the specific average nanofiber diameter is within a range from100 nm to 1000 nm, e.g., from 200 nm to 700 nm, and/or the specificrelative viscosity is within a range from 5 to 75, e.g., from 15 to 50or from 20 to 40, extruding a polyamide composition having a moisturecontent with a pressurized gas through a fiber forming channel having achannel temperature to form the polyamide nanofiber nonwoven having thetarget average nanofiber diameter and/or relative viscosity, andcontrolling the moisture content, the pressure of pressurized gas,and/or the channel temperature based on the specific average nanofiberdiameter and/or the specific relative viscosity. In one embodiment, themoisture content of the polyamide composition, i.e. starting resin, iscontrolled from 0.005 wt. % to 1 wt. %, e.g., from 0.005 wt. % to 0.5wt. %, from 0.02 to 0.3 wt. %, to target the specific average nanofiberdiameter and/or specific relative viscosity. The moisture content of thepolyamide composition may be controlled by drying the polyamidecomposition to have a moisture content of less than 0.02 wt. %, andrehydrating the dried polyamide composition. In one embodiment, thepressure of the pressurized gas is controlled to range from 160 kPa to220 kPa to target the specific average nanofiber diameter and/orspecific relative viscosity. In one embodiment, the channel temperature(die temperature), is controlled to range from 270° C. to 330° C., e.g.,from 270° C. to 315° C., to target the specific average nanofiberdiameter and/or specific relative viscosity. The fiber forming channelmay be a die and/or a capillary. In one embodiment, the polyamidenanofiber nonwoven is melt-blown and/or is free of solvent. In someembodiments, the polyamide composition may comprise a catalyst.

In another embodiment, the present disclosure is directed to a methodfor tuning the relative viscosity of a polyamide nanofiber nonwovencomprising the steps of targeting a specific relative viscosity for thepolyamide nanofiber nonwoven, wherein the specific relative viscosity iswithin a range from 5 to 75, e.g., from 15 to 50 or from 20 to 40,extruding a polyamide composition having a moisture content to form thepolyamide nanofiber nonwoven having the target relative viscosity, andcontrolling the moisture content based on the target relative viscosity.In one embodiment, the moisture content of the polyamide composition,i.e. starting resin, is controlled from 0.005 wt. % to 1 wt. %, e.g.,from 0.005 wt. % to 0.5 wt. %, from 0.02 to 0.3 wt. %, to target thespecific relative viscosity, for example a specific relative viscositywithin the range from 5 to 75, e.g., from 15 to 50 or from 20 to 40. Themoisture content of the polyamide composition may be controlled bydrying the polyamide composition to have a moisture content of less than0.02 wt. %, and rehydrating the dried polyamide composition. In oneembodiment, the polyamide composition may be extruded through a fiberforming channel having a channel temperature and the channel temperatureis controlled to range from 270° C. to 330° C. In one embodiment, thepolyamide nanofiber nonwoven is melt-blown and/or is free of solvent. Insome embodiments, the polyamide composition may comprise a catalyst.

In another embodiment, the present disclosure provides a method fortuning the nanofiber diameter of a polyamide nanofiber nonwovencomprising the steps of targeting a specific average nanofiber diameter,wherein the specific average nanofiber diameter is within a range from100 nm to 1000 nm, e.g., from 200 to 700 nm, extruding a polyamidecomposition with a pressurized gas to form the polyamide nanofibernonwoven having the target average nanofiber diameter, and controllingthe pressure of the pressurized gas based on the target averagenanofiber diameter. In one embodiment, the pressurized gas may becontrolled to range from 160 kPa to 220 kPa. In one embodiment, thepolyamide composition may be extruded through a fiber forming channelhaving a channel temperature and the channel temperature is controlledto range from 270° C. to 330° C. In one embodiment, the polyamidenanofiber nonwoven is melt-blown and/or is free of solvent. In someembodiments, the polyamide composition may comprise a catalyst. In oneembodiment, the moisture content of the polyamide composition, i.e.starting resin, is controlled from 0.005 wt. % to 1 wt. %, e.g., from0.005 wt. % to 0.5 wt. %, from 0.02 to 0.3 wt. %, target the specificaverage nanofiber diameter.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to thedrawings wherein like numerals designate similar parts and wherein:

FIG. 1 and FIG. 2 are separate schematic diagrams of a 2-phasepropellant-gas spinning system useful in connection with the presentinvention;

FIG. 3 is a photomicrograph of a nanofiber nylon 66 melt spun into anonwoven having an RV of 7.3 at a magnification of 50×; and

FIG. 4 is a photomicrograph of a nanofiber of a grade from FIG. 3 ofnylon 66 melt spun into a nonwoven having an RV of 7.3 at amagnification of 8000×; and

FIG. 5 is a schematic diagram of a melt blowing process in connectionwith embodiments of the present invention.

FIG. 6 is a photomicrograph of a nanofiber of nylon 66 with an RV of 36at a magnification of 100×.

FIG. 7 is a graph comparing thermal degradation index and oxidativedegradation index values for nanofiber samples as a function of dietemperature.

FIG. 8 is a graph comparing thermal degradation index and oxidativedegradation index values for nanofiber samples as a function of meterpump speed.

FIG. 9 is a graph demonstrating the tuning of product RV based on themoisture content of the polyamide composition.

FIG. 10 is a graph demonstrating the tuning of product RV based on themoisture content and channel temperatures.

FIG. 11 is a graph demonstrating the tuning of average nanofiberdiameter of the nonwoven product based on the air pressure and channeltemperatures.

DETAILED DESCRIPTION

Overview

As noted above, some conventional processes for producing nonwovens areknown. But these conventional techniques are either expensive and/orcannot obtain high production rates, e.g., electrospinning, or do nothave the ability to consistently form nanofibers, e.g., polyamidenanofibers, with acceptable fiber diameter distributions. Importantly,conventional processes do not provide the ability to tune, e.g., toadjust, control, or otherwise set properties and characteristics of theend product polyamide nanofiber nonwovens.

The inventors have now found that particular process parameters andconditions, e.g., moisture content of the polyamide, channeltemperature, pressure of the pressurized gas, and/or presence of acatalyst, can be employed to effectively and consistently obtainspecific desired properties and characteristics of the end productnonwoven. Beneficially, the tunable nature of the disclosed processesallow for a diversity of polyamide nanofiber nonwoven having desired,tuned characteristics. Further, the tunable nature of the disclosedprocesses, provides for added process flexibility and the ability toobtain tuned characteristics based on relationships of particularprocess parameters. Conventional processes did not contemplate theserelationships, and, as such, were unable to provide the aforementionedtunability.

The present disclosure is directed, in part, to a tunable method formaking a nanofiber nonwoven product and to the resultant products. Theproduct is formed by spinning a polyamide composition into a pluralityof nanofibers. The final product may be “tuned” by adjusting a varietyof conditions during the spinning process, and/or by adjusting the(precursor) polyamide composition so as to achieve one or more desirableproperties, such as average fiber diameter and Relative Viscosity (RV).

In some aspects, the average nanofiber diameter may be tuned bycontrolling a variety of conditions to a specific average nanofiberdiameter. In some aspects, the specific average nanofiber diameter ofthe product may be controlled to be from 100 to 1000 nanometers (nm),e.g., from 110 to 950 nm, 150 to 950 nm, from 115 to 925 nm, from 120 to900 nm, 150 to 900 nm, from 125 to 800 nm, from 150 to 800 nm, from 200to 800 nm, from 125 to 700 nm, from 200 to 700 nm, from 130 to 600 nm,from 250 to 650 nm, from 300 to 550 nm or from 150 to 500 nm (additionalaverage nanofiber diameter ranges and limits are provided herein).

In some aspects, the RV of the product may be tuned by controlling avariety of conditions to a specific RV. In some aspects, the specific RVof the product may be controlled to be from 2 to 330, e.g., from 2 to300, from 2 to 275, from 2 to 250, from 2 to 225, from 2 to 200, 2 to100, from 2 to 60, from 2 to 50, from 2 to 40, from 5 to 75, from 10 to40, 15 to 50, from 15 to 40, from 20 to 40 or from 20 to 38 (additionalRV ranges and limits are provided herein).

Conditions that may be adjusted during the spinning operation include,for example, channel temperature, air pressure, moisture content, and/orthe presence of the catalyst. By adjusting at least one of theseconditions, the RV of the product can be controlled, e.g., tuned to aspecific average nanofiber diameter and/or specific RV. For example, theRV of the product may be controlled, e.g., the RV is increased, remainsthe same, or is decreased, relative to the RV of the polyamidecomposition.

The present disclosure is also directed, in part, to a method for tuningcharacteristics of a polyamide nanofiber nonwoven. The method comprisesthe step of targeting a specific average fiber diameter and/or aspecific relative viscosity for the polyamide nanofiber nonwoven. Thespecific average nanofiber diameter may be within a range disclosedherein and/or the specific relative viscosity may be within a rangedisclosed herein. The method further comprises the steps of extruding apolyamide composition having a moisture content with a pressurized gasthrough a fiber forming channel having a channel temperature to form thepolyamide nanofiber nonwoven having the target average nanofiberdiameter and/or relative viscosity; and controlling the moisturecontent, the pressure of pressurized gas, and/or the channel temperaturebased on the specific average nanofiber diameter and/or the specificrelative viscosity.

The present disclosure is also directed, in part, to a method for tuningthe relative viscosity of a polyamide nanofiber nonwoven. The methodcomprises the step of targeting a specific relative viscosity for thepolyamide nanofiber nonwoven. The specific relative viscosity may bewithin a range disclosed herein. The method further comprises the stepsof extruding a polyamide composition having a moisture content to formthe polyamide nanofiber nonwoven having the target relative viscosity,and controlling the moisture content based on the target relativeviscosity.

The present disclosure is also directed, in part, to a method for tuningthe nanofiber diameter of a polyamide nanofiber nonwoven. The methodcomprises the step of targeting a specific average nanofiber diameter.The specific average nanofiber diameter may be within a range fromdisclosed herein. The method further comprises the steps of extruding apolyamide composition with a pressurized gas to form the polyamidenanofiber nonwoven having the target average nanofiber diameter, andcontrolling the pressure of the pressurized gas based on the targetaverage nanofiber diameter.

The present disclosure is also directed, in part, to polyamide nanofibernonwoven products, and methods of preparing the products, where from 1to 20% of the nanofiber diameters in the product are greater than 700nanometers. The method to form such products includes providing apolyamide composition having an RV from 2 to 330, spinning thecomposition at temperatures in the range of 215° C. to 315° C. to form aplurality of nanofibers, and forming the nanofibers into the product,wherein the product has an average nanofiber diameter from 100 to 1000nm, e.g., from 200 to 700 nm, and an RV from 2 to 330, e.g., from 5 to75, from 15 to 50 or from 20 to 40.

The present disclosure is also directed, in part, to polyamide nanofibernonwoven products formed by different spinning processes, wherein theselection of the equipment for the spinning process allows for one ormore desired properties of the product to be achieved. Such desiredproperties include average nanofiber diameter, nanofiber diameterdistribution, air permeability value, TDI, ODI, relative viscosity,filtration efficiency, and mean pore flow diameter. Additionally, the RVof the polyamide composition may optionally be adjusted, e.g., bychanging the ratio of amine end groups to carboxylic acid end groups inthe polyamide composition, to achieve the desired productproperty/properties.

The present disclosure is also directed, in part, to polyamide nanofibernonwoven products, and methods of preparing the products, where apolyamide composition having an initial RV is provided for spinning, oneor more desired properties for the product are chosen, the initial RV isadjusted based on at least one of the properties, the adjusted polyamidecomposition is spun into a plurality of nanofibers at a temperature, andthe nanofibers are formed into the product, wherein the product has anaverage nanofiber diameter disclosed herein and an RV disclosed herein.The one or more desired properties may be average nanofiber diameter,nanofiber diameter distribution, air permeability value, TDI, ODI,relative viscosity, mean pore flow diameter, and filtration efficiency.

The polyamide composition, also referred to herein as a polyamide, maybe spun or melt blown into fibers, e.g., nanofibers. The polyamidenanofibers may have an average diameter of less than 1000 nanometers (1micron) and may be formed into the nonwoven product. Traditional meltspinning techniques have been unable to form fibers having low averagediameters, e.g., nanofibers. Typical melt spun fiber average diametersare at least 1 micron and cannot achieve the surface area to volumeratio that a nanofiber can achieve. Such an increased surface area tovolume ratio is beneficial in many applications.

In some embodiments, the nanofiber nonwoven product is generallyproduced by: (a) providing a (spinnable) polyamide composition, whereinthe polyamide composition has the RV discussed herein; (b) spinning thepolyamide composition into a plurality of nanofibers having an averagefiber diameter of less than 1 micron by way of a process directed to2-phase propellant-gas spinning, including extruding the polyamidecomposition in liquid form with pressurized gas through a fiber-formingchannel, and (c) forming the nanofibers into the nanofiber nonwovenproduct. The general process is illustrated in FIGS. 1 and 2.

The inventors have discovered that the characteristics of the precursorpolyamide can be adjusted by utilizing particular parameters such that adesirable end product can be achieved. These specific relationshipsbetween polyamide composition, operating conditions, and end productshave not yet been sufficiently explored and/or disclosed in the existingreferences.

Particularly preferred polyamides include nylon 66, as well ascopolymers, blends, and alloys of nylon 66 with nylon 6.

Other embodiments include nylon derivatives, copolymers, terpolymers,blends and alloys containing or prepared from nylon 66 or nylon 6,copolymers or terpolymers with the repeat units noted above includingbut not limited to: N6T/66, N612, N6/66, N6I/66, N11, and N12, wherein“N” means Nylon, “T” means “terephthalic acid”, and “I” meansisophthalic acid. Another preferred embodiment includes High TemperatureNylons (“HTN”) as well as blends, derivatives, copolymers or terpolymerscontaining them. Furthermore, another preferred embodiment includes longchain aliphatic polyamide made with long chain diacids as well asblends, derivatives or copolymers containing them.

FIG. 1 illustrates an exemplary technique wherein a 2 phase propellantgas spinning process may be used for making the nanofiber. FIG. 2illustrates a general melt blowing technique.

In particular, disclosed herein is an embodiment wherein a method ofmaking a nanofiber nonwoven product wherein the nonwoven fabric ismelt-spun by way of melt-blowing through a spinneret into a highvelocity gaseous stream. More particularly, in one embodiment, thenonwoven fabric is melt-spun by 2-phase propellant-gas spinning,including extruding the polyamide composition in liquid form withpressurized gas through a fiber-forming channel. Further embodimentsdisclose additional methods and equipment that may be used in themethods to form the desired product.

In one embodiment, the channel temperature of the fiber-forming channelmay be controlled to tune a characteristics of the nanofiber nonwovenproduct. The fiber-forming channel may be a die and/or a capillary, andthe channel temperature may be referred to as the die temperature. Inone embodiment, the channel temperature may range from 270° C. to 330°C., e.g., from 275° C. to 320° C. or from 280° C. to 310° C.

Definitions and Test Methods

Terminology used herein is given its ordinary meaning consistent withthe definitions set forth below; GSM refers to basis weight in grams persquare meter (g/m²), RV refers to Relative Viscosity and so forth.

Percentages, parts per million (ppm) and the like refer to weightpercent or parts by weight based on the weight of the composition unlessotherwise indicated.

Typical definitions and test methods are further recited in US Pub. Nos.2015/0107457 and 2015/0111019. The term “nanofiber nonwoven product” forexample, refers to a web of a multitude of essentially randomly orientednanofibers where no overall repeating structure can be discerned by thenaked eye in the arrangement of nanofibers. The nanofibers can be bondedto each other, or can be entangled and not bonded to impart strength andintegrity to the web. The nanofibers can be staple nanofibers orcontinuous nanofibers, and can comprise a single material or a multitudeof materials, either as a combination of different nanofibers or as acombination of similar nanofibers each comprising of differentmaterials. The nanofiber nonwoven product is constructed predominantlyof nanofibers. “Predominantly” means that greater than 50% of the fibersin the web are nanofibers. The term “nanofiber” refers to fibers havinga number average diameter less than 1000 nm or 1 micron. In the case ofnonround cross-sectional nanofibers, the term “diameter” as used hereinrefers to the greatest cross-sectional dimension.

Basis Weight may be determined by ASTM D-3776 and reported in g/m².

“Consisting essentially of” and like terminology refers to the recitedcomponents and excludes other ingredients which would substantiallychange the basic and novel characteristics of the composition orarticle. Unless otherwise indicated or readily apparent, a compositionor article consists essentially of the recited or listed components whenthe composition or article includes 90% or more by weight of the recitedor listed components. That is, the terminology excludes more than 10%unrecited components.

To the extent not indicated otherwise, test methods for determiningaverage fiber diameters, are as indicated in Hassan et al., J ofMembrane Sci., 427, 336-344, 2013, unless otherwise specified.

Air permeability is measured using an Air Permeability Tester, availablefrom Precision Instrument Company, Hagerstown, Md. Air permeability isdefined as the flow rate of air at 23±1° C. through a sheet of materialunder a specified pressure head. It is usually expressed as cubic feetper minute per square foot at 0.50 in. (12.7 mm) water pressure, in cm³per second per square cm or in units of elapsed time for a given volumeper unit area of sheet. The instrument referred to above is capable ofmeasuring permeability from 0 to approximately 5000 cubic feet perminute per square foot of test area. For purposes of comparingpermeability, it is convenient to express values normalized to 5 GSMbasis weight. This is done by measuring Air Permeability Value and basisweight of a sample (@ 0.5″ H₂O typically), then multiplying the actualAir Permeability Value by the ratio of actual basis weight in GSM to 5.For example, if a sample of 15 GSM basis weight has a Value of 10CFM/ft², its Normalized 5 GSM Air Permeability Value is 30 CFM/ft².

Polyamide

As used herein, polyamide composition and like terminology refers tocompositions containing polyamides including copolymers, terpolymers,polymer blends, alloys and derivatives of polyamides. Further, as usedherein, a “polyamide” refers to a polymer, having as a component, apolymer with the linkage of an amino group of one molecule and acarboxylic acid group of another molecule. In some aspects, thepolyamide is the component present in the greatest amount. For example,a polyamide containing 40 wt. % nylon 6, 30 wt. % polyethylene, and 30wt. % polypropylene is referred to herein as a polyamide since the nylon6 component is present in the greatest amount. Additionally, a polyamidecontaining 20 wt. % nylon 6, 20 wt. % nylon 66, 30 wt. % polyethylene,and 30 wt. % polypropylene is also referred to herein as a polyamidesince the nylon 6 and nylon 66 components, in total are the componentspresent in the greatest amount.

Exemplary polyamides and polyamide compositions are described inKirk-Othmer, Encyclopedia of Chemical Technology, Vol. 18, pp. 328371(Wiley 1982), the disclosure of which is incorporated by reference.

Briefly, polyamides are generally known as compounds that containrecurring amide groups as integral parts of the main polymer chains.Linear polyamides are of particular interest and may be formed fromcondensation of bifunctional monomers. Polyamides are frequentlyreferred to as nylons. Although they generally are considered ascondensation polymers, polyamides also are formed by additionpolymerization. This method of preparation is especially important forsome polymers in which the monomers are cyclic lactams, e.g., Nylon 6.Particular polymers and copolymers and their preparation are seen in thefollowing patents: U.S. Pat. Nos. 4,760,129; 5,504,185; 5,543,495;5,698,658; 6,011,134; 6,136,947; 6,169,162; 7,138,482; 7,381,788; and8,759,475.

There are numerous advantages of using polyamides, also known asspecifically nylons, in commercial applications. Nylons are generallychemical and temperature resistant, resulting in superior performance toother particles. They are also known to have improved strength,elongation, and abrasion resistance as compared to other polymers.Nylons are also very versatile, allowing for their use in a variety ofapplications.

A class of polyamides particularly preferred for some applicationsincludes High Temperature Nylons (HTN's) as are described in Glasscocket al., High Performance Polyamides Fulfill Demanding Requirements forAutomotive Thermal Management Components, (DuPont),http://www2.dupont.com/Automotive/en_US/assets/downloads/knowledge%20center/HTN-whitepaper-R8.pdfavailable online Jun. 10, 2016. Such polyamides typically include one ormore of the structures seen in the following:

Non-limiting examples of polymers included in the polyamides includepolyamides, polypropylene and copolymers, polyethylene and copolymers,polyesters, polystyrenes, polyurethanes, and combinations thereof.Thermoplastic polymers and biodegradable polymers are also suitable formelt blowing or melt spinning into nanofibers of the present invention.As discussed herein, the polymers may be melt spun or melt blown, with apreference for melt spinning or melt blowing by 2-phase propellant-gasspinning, including extruding the polyamide composition in liquid formwith pressurized gas through a fiber-forming channel.

Melt points of nylon nanofiber products described herein, includingcopolymers and terpolymers, may be between 223° C. and 390° C., e.g.,from 223° C. to 380° C., or from 225° C. to 350° C. Additionally, themelt point may be greater than that of conventional nylon 66 melt pointsdepending on any additional polymer materials that are added.

Other polymer materials that can be used in the polyamide nanofibernonwovens of the invention include both addition polymer andcondensation polymer materials such as polyolefin, polyacetal, polyamide(as previously discussed), polyester, cellulose ether and ester,polyalkylene sulfide, polyarylene oxide, polysulfone, modifiedpolysulfone polymers and mixtures thereof. Preferred materials that fallwithin these generic classes include polyamides, polyethylene,polybutylene terephthalate (PBT), polypropylene, poly(vinylchloride),polymethylmethacrylate (and other acrylic resins), polystyrene, andcopolymers thereof (including ABA type block copolymers),poly(vinylidene fluoride), poly(vinylidene chloride), polyvinylalcoholin various degrees of hydrolysis (87% to 99.5%) in crosslinked andnon-crosslinked forms. Addition polymers tend to be glassy (a Tg greaterthan room temperature). This is the case for polyvinylchloride andpolymethylmethacrylate, polystyrene polymer compositions or alloys orlow in crystallinity for polyvinylidene fluoride and polyvinylalcoholmaterials. Nylon copolymers embodied herein, can be made by combiningvarious diamine compounds, various diacid compounds and various cycliclactam structures in a reaction mixture and then forming the nylon withrandomly positioned monomeric materials in a polyamide structure. Forexample, a nylon 66-6,10 material is a nylon manufactured fromhexamethylene diamine and a C6 and a C10 blend of diacids. A nylon6-66-6,10 is a nylon manufactured by copolymerization ofepsilonaminocaproic acid, hexamethylene diamine and a blend of a C6 anda C10 diacid material.

In some embodiments, such as that described in U.S. Pat. No. 5,913,993,a small amount of polyethylene polymer can be blended with a nyloncompound used to form a nanofiber nonwoven fabric with desirablecharacteristics. The addition of polyethylene to nylon enhances specificproperties such as softness. The use of polyethylene also lowers cost ofproduction, and eases further downstream processing such as bonding toother fabrics or itself. The improved fabric can be made by adding asmall amount of polyethylene to the nylon feed material used inproducing a nanofiber melt blown fabric. More specifically, the fabriccan be produced by forming a blend of polyethylene and nylon 66,extruding the blend in the form of a plurality of continuous filaments,directing the filaments through a die to melt blow the filaments,depositing the filaments onto a collection surface such that a web isformed.

The polyethylene useful in the process of this embodiment of the subjectinvention preferably has a melt index between about 5 grams/10 min andabout 200 grams/10 min and, more preferably, between about 17 grams/10min and about 150 grams/10 min. The polyethylene should preferably havea density between about 0.85 grams/cc and about 1.1 grams/cc and, mostpreferably between about 0.93 grams/cc and about 0.95 grams/cc. Mostpreferably, the melt index of the polyethylene is about 150 and thedensity is about 0.93.

The polyethylene used in the process of this embodiment of the subjectinvention can be added at a concentration of about 0.05% to about 20%.In a preferred embodiment, the concentration of polyethylene will bebetween about 0.1% and about 1.2%. Most preferably, the polyethylenewill be present at about 0.5%. The concentration of polyethylene in thefabric produced according to the method described will be approximatelyequal to the percentage of polyethylene added during the manufacturingprocess. Thus, the percentage of polyethylene in the fabrics of thisembodiment of the subject invention will typically range from about0.05% to about 20% and will preferably be about 0.5%. Therefore, thefabric will typically comprise between about 80 and about 99.95 wt. % ofnylon. The filament extrusion step can be carried out between about 250°C. and about 325° C. Preferably, the temperature range is about 280° C.to about 315° C. but may be lower if nylon 6 is used.

The blend or copolymer of polyethylene and nylon can be formed in anysuitable manner. Typically, the nylon compound will be nylon 66;however, other polyamides of the nylon family can be used. Also,mixtures of nylons can be used. In one specific example, polyethylene isblended with a mixture of nylon 6 and nylon 66. The polyethylene andnylon polymers are typically supplied in the form of pellets, chips,flakes, and the like. The desired amount of the polyethylene pellets orchips can be blended with the nylon pellets or chips in a suitablemixing device such as a rotary drum tumbler or the like, and theresulting blend can be introduced into the feed hopper of theconventional extruder or the melt blowing line. The blend or copolymercan also be produced by introducing the appropriate mixture into acontinuous polymerization spinning system.

Further, differing species of a general polymeric genus can be blended.For example, a high molecular weight styrene material can be blendedwith a low molecular weight, high impact polystyrene. A Nylon-6 materialcan be blended with a nylon copolymer such as a Nylon-6; 66; 6,10copolymer. Further, a polyvinylalcohol having a low degree of hydrolysissuch as a 87% hydrolyzed polyvinylalcohol can be blended with a fully orsuperhydrolyzed polyvinylalcohol having a degree of hydrolysis between98 and 99.9% and higher. All of these materials in admixture can becrosslinked using appropriate crosslinking mechanisms. Nylons can becrosslinked using crosslinking agents that are reactive with thenitrogen atom in the amide linkage. Polyvinyl alcohol materials can becrosslinked using hydroxyl reactive materials such as monoaldehydes,such as formaldehyde, ureas, melamine-formaldehyde resin and itsanalogues, boric acids and other inorganic compounds, dialdehydes,diacids, urethanes, epoxies and other known crosslinking agents.Crosslinking technology is a well-known and understood phenomenon inwhich a crosslinking reagent reacts and forms covalent bonds betweenpolymer chains to substantially improve molecular weight, chemicalresistance, overall strength and resistance to mechanical degradation.

One preferred mode of the invention is a polyamide comprising a firstpolymer and a second, but different polymer (differing in polymer type,molecular weight or physical property) that is conditioned or treated atelevated temperature. The polymer blend can be reacted and formed into asingle chemical specie or can be physically combined into a blendedcomposition by an annealing process. Annealing implies a physicalchange, like crystallinity, stress relaxation or orientation. Preferredmaterials are chemically reacted into a single polymeric specie suchthat a Differential Scanning calorimeter (DSC) analysis reveals a singlepolymeric material to yield improved stability when contacted with hightemperature, high humidity and difficult operating conditions. Preferredmaterials for use in the blended polymeric systems include nylon 6;nylon 66; nylon 6,10; nylon (6-66-6,10) copolymers and other lineargenerally aliphatic nylon compositions.

A suitable polyamide may include for example, 20% nylon 6, 60% nylon 66and 20% by weight of a polyester. The polyamide may include combinationsof miscible polymers or combinations of immiscible polymers.

In some aspects, the polyamide may include nylon 6. In terms of lowerlimits, the polyamide may include nylon 6 in an amount of at least 0.1wt. %, e.g., at least 1 wt. %, at least 5 wt. %, at least 10 wt. %, atleast 15 wt. %, or at least 20 wt. %. In terms of upper limits, thepolyamide may include nylon 6 in an amount of 99.9 wt. % or less, 99 wt.% or less, 95 wt. % or less, 90 wt. % or less, 85 wt. % or less, or 80wt. % or less. In terms of ranges, the polyamide may comprise nylon 6 inan amount from 0.1 to 99.9 wt. %, e.g., from 1 to 99 wt. %, from 5 to 95wt. %, from 10 to 90 wt. %, from 15 to 85 wt. %, or from 20 to 80 wt. %.

In some aspects, the polyamide may include nylon 66. In terms of lowerlimits, the polyamide may include nylon 66 in an amount of at least 0.1wt. %, e.g., at least 1 wt. %, at least 5 wt. %, at least 10 wt. %, atleast 15 wt. %, or at least 20 wt. %. In terms of upper limits, thepolyamide may include nylon 66 in an amount of 99.9 wt. % or less, 99wt. % or less, 95 wt. % or less, 90 wt. % or less, 85 wt. % or less, or80 wt. % or less. In terms of ranges, the polyamide may comprise nylon66 in an amount from 0.1 to 99.9 wt. %, e.g., from 1 to 99 wt. %, from 5to 95 wt. %, from 10 to 90 wt. %, from 15 to 85 wt. %, or from 20 to 80wt. %.

In some aspects, the polyamide may include nylon 6T. In terms of lowerlimits, the polyamide may include nylon 6I in an amount of at least 0.1wt. %, e.g., at least 0.5 wt. %, at least 1 wt. %, at least 5 wt. %, atleast 7.5 wt. %, or at least 10 wt. %. In terms of upper limits, thepolyamide may include nylon 6I in an amount of 50 wt. % or less, 40 wt.% or less, 35 wt. % or less, 30 wt. % or less, 25 wt. % or less, or 20wt. % or less. In terms of ranges, the polyamide may comprise nylon 6Iin an amount from 0.1 to 50 wt. %, e.g., from 0.5 to 40 wt. %, from 1 to35 wt. %, from 5 to 30 wt. %, from 7.5 to 25 wt. %, or from 10 to 20 wt.%.

In some aspects, the polyamide may include nylon 6T. In terms of lowerlimits, the polyamide may include nylon 6T in an amount of at least 0.1wt. %, e.g., at least 1 wt. %, at least 5 wt. %, at least 10 wt. %, atleast 15 wt. %, or at least 20 wt. %. In terms of upper limits, thepolyamide may include nylon 6T in an amount of 50 wt. % or less, 47.5wt. % or less, 45 wt. % or less, 42.5 wt. % or less, 40 wt. % or less,or 37.5 wt. % or less. In terms of ranges, the polyamide may comprisenylon 6T in an amount from 0.1 to 50 wt. %, e.g., from 1 to 47.5 wt. %,from 5 to 45 wt. %, from 10 to 42.5 wt. %, from 15 to 40 wt. %, or from20 to 37.5 wt. %.

Block copolymers are also useful in the process of this invention. Withsuch copolymers the choice of solvent swelling agent is important. Theselected solvent is such that both blocks were soluble in the solvent.One example is an ABA (styrene-EP-styrene) or AB (styrene-EP) polymer inmethylene chloride solvent. If one component is not soluble in thesolvent, it will form a gel. Examples of such block copolymers areKraton® type of styrene-b-butadiene and styrene-b-hydrogenated butadiene(ethylene propylene), Pebax® type of e-caprolactam-b-ethylene oxide,Sympatex® polyester-b-ethylene oxide and polyurethanes of ethylene oxideand isocyanates.

Addition polymers like polyvinylidene fluoride, syndiotacticpolystyrene, copolymer of vinylidene fluoride and hexafluoropropylene,polyvinyl alcohol, polyvinyl acetate, amorphous addition polymers, suchas poly(acrylonitrile) and its copolymers with acrylic acid andmethacrylates, polystyrene, poly(vinyl chloride) and its variouscopolymers, poly(methyl methacrylate) and its various copolymers, areknown to be solution spun with relative ease because they are soluble atlow pressures and temperatures. It is envisioned these can be melt spunper the instant invention as one method of making nanofibers.

There is a substantial advantage to forming polymeric compositionscomprising two or more polymeric materials in polymer admixture, alloyformat or in a crosslinked chemically bonded structure. We believe suchpolymer compositions improve physical properties by changing polymerattributes such as improving polymer chain flexibility or chainmobility, increasing overall molecular weight and providingreinforcement through the formation of networks of polymeric materials.

In one embodiment of this concept, two related polymer materials can beblended for beneficial properties. For example, a high molecular weightpolyvinylchloride can be blended with a low molecular weightpolyvinylchloride. Similarly, a high molecular weight nylon material canbe blended with a low molecular weight nylon material.

RV and Fiber Diameter Targets

As explained above, channel temperature, pressure of the pressurizedgas, moisture content, and/or the presence of a catalyst may be adjustedor controlled to adjust the nanofiber diameter and/or RV of the productto a targeted (specific) nanofiber diameter and/or RV.

RV

In some embodiments, the RV of the nonwoven may be tuned to a targeted(specific) RV. RV of polyamides refers to the ratio of solution orsolvent viscosities measured in a capillary viscometer at 25° C. (ASTM D789). For present purposes the solvent is formic acid containing 10 wt.% water and 90 wt. % formic acid. The solution is 8.4 wt. % polymerdissolved in the solvent.

In some embodiments, the targeted specific RV of the nanofiber nonwovenproduct has a lower limit of at least 2, e.g., at least 3, at least 4,at least 5, at least 10, at least 15, at least 20, or at least 25. Interms of upper limits, the nonwoven product may have an RV of 330 orless, 300 or less, 275 or less, 250 or less, 225 or less, 200 or less,150 or less, 100 or less, 75 or less, 60 or less, 50 or less, 40 orless, or 38 or less. In terms of ranges, the nonwoven product may havean RV ranging from 2 to 330, e.g., from 2 to 300, from 2 to 275, from 2to 250, from 2 to 225, from 2 to 200, 2 to 100, from 2 to 60, from 2 to50, from 2 to 40, from 5 to 75, from 10 to 40, 15 to 50, from 15 to 40,from 20 to 40 or from 20 to 38, and any values in between.

The relationship between the RV of the polyamide composition and the RVof the nanofiber nonwoven product may vary. In some aspects, the RV ofthe nanofiber nonwoven product may be lower than the RV of the polyamidecomposition. Reducing the RV conventionally has not been a desirablepractice when spinning nylon 66. The inventors, however, have discoveredthat, in the production of nanofibers, it is an advantage. It has beenfound that the use of lower RV polyamide nylons, e.g., lower RV nylon66, in a melt spinning process has surprisingly been found to yieldnanofiber filaments having unexpectedly small filament diameters.

In some embodiments, the RV of the polyamide, e.g., starting resin, hasa lower limit of at least 2, e.g., at least 3, at least 4, or at least5. In terms of upper limits, the polyamide has an RV of at 330 or less,300 or less, 275 or less, 250 or less, 225 or less, 200 or less, 150 orless, 100 or less, or 60 or less. In terms of ranges, the polyamide mayhave an RV of 2 to 330, e.g., from 2 to 300, from 2 to 275, from 2 to250, from 2 to 225, from 2 to 200, 2 to 100, from 2 to 60, from 2 to 50,from 2 to 40, from 10 to 40, or from 15 to 40 and any values in between.

In some aspects, the RV of the nanofiber nonwoven product is at least20% less than the RV of the polyamide prior to spinning, e.g., at least25% less, at least 30% less, at least 35% less, at least 40% less, atleast 45% less, or at least 90% less.

In other aspects, the RV of the nanofiber nonwoven product is at least5% greater than the RV of the polyamide prior to spinning, e.g., atleast 10% greater, at least 15% greater, at least 20% greater, at least25% greater, at least 30% greater, or at least 35% greater.

In still further aspects, the RV of the polyamide and the RV of thenanofiber nonwoven product may be substantially the same, e.g., within5% of each other.

The RV, (ηr), is the ratio of the absolute viscosity of the polymersolution to that of the formic acid:η_(r)=(η_(p)/η_(f))=(f _(r) ×d _(p) ×t _(p))/η_(f), where: d_(p)=density of formic acid-polymer solution at 25° C.,

-   -   t_(p)=average efflux time for formic acid-polymer solution,    -   η_(f)=absolute viscosity of formic acid, kPa×s(E+6 cP) and    -   f_(r)=viscometer tube factor, mm²/s (cSt)/s=η_(r)/t₃.

A typical calculation for a 50 RV specimen:ηr=(fr×dp×tp)/ηf, where:

-   -   fr=viscometer tube factor, typically 0.485675 cSt/s    -   dp=density of the polymer—formic solution, typically 1.1900 g/ml    -   tp=average efflux time for polymer—formic solution, typically        135.00 s    -   ηf=absolute viscosity of formic acid, typically 1.56 cP

giving an RV of ηr=(0.485675 cSt/s×1.1900 g/ml×135.00 s)/1.56 cP=50.0.The term t₃ is the efflux time of the S-3 calibration oil used in thedetermination of the absolute viscosity of the formic acid as requiredin ASTM D789 (2015).

Fiber Diameter, Distributions, Equipment

In some embodiments, the average fiber diameter of the nonwoven may betuned to a targeted (specific) average fiber diameter. The fibers (ofthe nonwovens) disclosed herein may be nanofibers, e.g., fibers havingan average fiber diameter of less than or equal to 1000 nm. Although thepresent disclosure is generally directed to nanofibers, the tunableaspects of the present disclosure are applicable to fibers havinggreater fiber diameters, e.g., fiber diameters of 1000 nm or greater.

In one embodiment, the targeted specific average nanofiber diameter isless than or equal to 1000 nm, e.g., less than or equal to 950 nm, lessthan or equal to 925 nm, less than or equal to 900 nm, less than orequal to 800 nm, less than or equal to 700 nm, less than or equal to 600nm, or less than or equal to 500 nm. In terms of lower limits, thespecific average nanofiber diameter may be at least 100 nm, at least 110nm, at least 115 nm, at least 120 nm, at least 125 nm, at least 130 nm,at least 150 nm, at least 200 nm, at least 250 nm or at least 300 nm. Interms of ranges, the specific average nanofiber diameter range from 100to 1000 nm, e.g., from 110 to 950 nm, 150 to 950 nm, from 115 to 925 nm,from 120 to 900 nm, 150 to 900 nm, from 125 to 800 nm, from 300 to 850nm, from 150 to 800 nm, from 200 to 800 nm, from 125 to 700 nm, from 200to 700 nm, from 350 to 700 nm, from 400 to 700 nm, from 130 to 600 nm,from 250 to 650 nm, from 300 to 550 nm or from 150 to 500 nm. Suchaverage nanofiber diameters differentiate the nanofibers formed by thespinning processes disclosed herein from nanofibers formed byelectrospinning processes. Electrospinning processes typically producenonwovens having average fiber diameters that are smaller thanmelt-blown processes. The size of nanofibers produced by electrospinningmay vary, and includes fiber diameters of less than 100 nm, e.g., from50 to less than 100 nm. Without being bound by theory, it is believedthat such small nanofiber diameters may result in reduced strength ofthe fibers and increased difficulty in handling the nanofibers.

The use of the disclosed process and precursors leads to a specific andbeneficial distribution of fiber diameters. For example, less than 20%of the nanofibers may have a fiber diameter from greater than 700 nm,e.g., less than 17.5%, less than 15%, less than 12.5%, or less than 10%.In terms of lower limits, at least 1% of the nanofibers have a fiberdiameter of greater than 700 nanometers, e.g., at least 2%, at least 3%,at least 4%, or at least 5%. In terms of ranges, from 1 to 20% of thenanofibers have a fiber diameter of greater than 700 nanometers, e.g.,from 2 to 17.5%, from 3 to 15%, from 4 to 12.5%, or from 5 to 10%. Sucha distribution differentiates the nanofiber nonwoven products describedherein from those formed by electrospinning (which have a smalleraverage diameter and a much narrower distribution) and from those formedby non-nanofiber melt spinning (which have a much greater distribution).For example, a non-nanofiber centrifugally spun nonwoven is disclosed inWO 2017/214085 and reports fiber diameters of 2.08 to 4.4 microns butwith a very broad distribution reported in FIG. 10A of WO 2017/214085.

The product having the nanofiber distribution described herein may beformed by providing a polyamide composition having a RV from 2 to 330,spinning the polyamide composition at a channel temperature in the rangedisclosed herein to form a plurality of nanofibers, and forming thenanofibers into the nanofiber nonwoven product, wherein the product hasa specific average nanofiber diameter disclosed herein, and/or aspecific RV disclosed herein, and from 1 to 20% of nanofibers having adiameter of greater than 700 nanometers, including further ranges andlimits disclosed herein. During the production of the nanofibers, it hassurprisingly and unexpectedly been found that the nanofiber diameterdistribution and the average nanofiber diameter do not substantiallychange when the throughput of the polyamide composition through thespinning process is changed. For example, changing the throughput ratethrough a die or capillary does not substantially change the nanofiberdistribution or average diameter, e.g., a change of less than 10% isseen, less than 5%, less than 1%, or less than 0.5%. Thus lack ofresponse to a change in throughput is advantageous because it allows forthe adjustment of other product features, such as basis weight, withoutalso having to account for changes in average diameter or nanofiberdiameter distribution.

Without being bound by theory, it is believed that other changes to themethod do allow for the average nanofiber diameter and/or the nanofiberdiameter distribution to be adjusted. In some aspects, the number ofholes per inch in the die or capillary is adjusted. In some aspects, thesize of the holes in the die or capillary is adjusted. In still furtheraspects, the holdup time in the spinning process may be adjusted. Insome aspects, the flow characteristics of the polyamide compositionthrough the die or capillary may be adjusted. In some aspects, nylon 6or other polyamides may be added to the polyamide composition.Additionally, further modifications in the equipment used may influencethe average nanofiber diameter and/or the nanofiber diameterdistribution. Equipment such as that described in U.S. Pat. Nos.7,300,272; 8,668,854; and 8,658,067, the entireties of which areincorporated by reference herein, may be used. Briefly, U.S. Pat. No.7,300,272 discloses equipment comprising a fiber extrusion packincluding a number of split distribution plates arranged in a stack toform a distribution network. U.S. Pat. No. 8,668,854 discloses atwo-phase flow nozzle and a converging channel, wherein the convergingchannel accelerates the polyamide composition from the two-phase flownozzle to a channel exit to form a polymeric film along the surface ofthe converging channel, wherein the polymeric film is fibrillated at thechannel exit to form the nanofibers; and collecting the nanofibers toform the product. U.S. Pat. No. 8,658,067 discloses a fiber producingdevice comprising a body configured to receive the polyamidecomposition, a driver capable of rotating the body, a deposition systemfor directing nanofibers formed in the body toward a substrate, and asubstrate transfer system for moving substrate material through adeposition system for directing the nanofibers to the substrate. In yetanother aspect, in the melt blown process the orientation of the airrelative to the exit of the polymer from the capillaries in the die maybe modified.

An additional embodiment of the present invention involves production ofa layer of filter media comprising polyamide nanofibers having thespecific average fiber diameter and/or having the specific RV disclosedherein. In this alternate embodiment, some RV ranges include: 2 to 330,e.g., from 2 to 300, from 2 to 275, from 2 to 250, from 2 to 225, from 2to 200, 2 to 100, from 2 to 60, from 2 to 50, from 2 to 40, from 10 to40, or from 15 to 40. The nanofibers are subsequently converted tononwoven web. As the RV increases beyond about 20 to 30, operatingtemperature becomes a greater parameter to consider. At an RV above therange of about 20 to 30, the temperature must be carefully controlled soas the polymer melts for processing purposes. Methods or examples ofmelt techniques are described in U.S. Pat. No. 8,777,599, as well asheating and cooling sources which may be used in the apparatuses toindependently control the temperature of the fiber producing device. Nonlimiting examples include resistance heaters, radiant heaters, cold gasor heated gas (air or nitrogen), or conductive, convective, or radiationheat transfer mechanisms.

Moisture Content, Temperature, Pressure, End Groups, Catalyst, andTunability

As noted above, the targeted (specific) nanofiber diameter and/or RV maybe tuned by adjusting or controlling the disclosed parameters, e.g.,channel temperature, pressure of the pressurized gas, moisture content,and/or the presence of a catalyst.

Moisture Content

The inventors have discovered that, beneficially, the RV of thepolyamide, e.g., the nylon 66, may be tuned, e.g., lowered, bydepolymerizing the polymer with the addition of moisture. Up to 3%moisture, e.g., from 0.0005 to 3 wt. %, from 0.005 to 1 wt. %, from0.005 to 0.5 wt. %, may be included before the polyamide begins tohydrolyze. This technique provides a surprising advantage over theconventional method of adding other polymers, e.g., polypropylene, tothe polyamide. As discussed further herein, the moisture content mayalso be adjusted (optionally in combination with adjusting the ratio ofthe end groups) to keep the reaction equilibrium constant the same.

In some aspects, the RV of the nonwoven product may be tuned, e.g., bylowering the temperature and/or by reducing the moisture content of thepolyamide composition, e.g., starting resin. In some cases, temperaturemay have a relatively modest effect on adjusting the RV, as compared tomoisture content of the polyamide composition.

The moisture may be adjusted within the range of 0.0005 to 3 wt. %.,e.g., from 0.005 to 1 wt. %, from 0.005 to 0.5 wt. %, or from 0.02 to0.3 wt. %, and all ranges within, as described herein. In some aspects,the moisture content may be raised within this range to lower the RV ofthe product relative to the RV of the polyamide composition. In someaspects, the moisture content may be lowered within this range to raisethe RV of the product relative to the RV of the polyamide composition.

In some embodiments, the moisture content of the polyamide compositionmay be tuned to achieve the desired end product nonwovencharacteristic(s). For example the moisture content may be controlled tohave a lower value that is greater than or equal to 0.0001 wt. %, e.g.,greater than or equal to 0.0005 wt. %, greater than or equal to 0.001wt. %, greater than or equal to 0.005 wt. %, greater than or equal to0.01 wt. %, greater than or equal to 0.02 wt. %, greater than or equalto 0.05 wt. %, greater than or equal to 0.1 wt. %, or greater than orequal to 0.25 wt. %. In some aspects, up to 5 wt. % moisture, e.g., upto 4 wt. %, up to 3 wt. %, up to 2 wt. %, up to 1 wt. %, up to 0.75 wt.%, up to 0.5 wt. %, up to 0.4 wt. %, or up to 0.3 wt. %. may be includedbefore the polyamide begins to hydrolyze. In terms of ranges, themoisture content may range from 0.0005 to 5 wt. %, e.g., from 0.001 to 4wt. %, from 0.01 to 3 wt. %, from 0.25 to 2 wt. %, from 0.25 to 1 wt. %,from 0.25 to 0.6 wt. %, from 0.005 to 1 wt. %, from 0.005 to 0.5 wt. %,from 0.02 to 0.3 wt. % or from 0.1 to 0.3 wt. %. Reduction of moisturecontent is also advantageous for decreasing TDI and ODI values, asdiscussed further herein.

The moisture content may be adjusted by selecting a polyamidecomposition with the desired moisture content. Commercially availablepolyamide compositions may have a moisture content that ranges from 0.25to 0.6 wt. %.

In one embodiment, the moisture content may be adjusted by drying thepolyamide composition to essentially dry, or having a moisture contentof less than 0.02 wt. %, e.g., less than 0.001 wt. %, less than 0.0005wt. %, or less than 0.0001 wt. %.

To control the moisture content, the polyamide composition may berehydrated to the desired moisture content. This may be done prior tofeeding the polyamide to the extruder. In one embodiment, the moistureadjustment may be done during extrusion.

Channel Temperature

The inventors have discovered that process temperatures, such as channeltemperature, may be tuned (optionally in combination with otherparameters) to achieve the targeted (specific) nanofiber diameter and/orRV.

In one embodiment, process temperature, such as channel temperature, maybe raised to lower the RV. In some embodiments, however, a processtemperature raise may only slightly lower the RV since temperatureaffects the kinetics of the reaction, but not the reaction equilibriumconstant.

In some embodiments, the moisture content of the polyamide compositionmay be tuned to achieve the desired end product nonwovencharacteristic(s). For example the moisture content may be controlled tohave a lower value that is greater 0.02 wt. %.

In one embodiment, the channel temperature (or die temperature) may betuned to achieve the desired end product nonwoven characteristic(s). Forexample, channel temperature may be controlled to be within the rangefrom 215° C. to 330° C., e.g., from 250° C. to 330° C., from 270° C. to325° C., from 250° C. to 315° C., from 270° C. to 315° C., from 215° C.to 315° C., from 225° C. to 300° C., from 235° C. to 290° C., or from250° C. to 280° C. In some aspects, the channel temperature has a lowerlimit of 215° C., e.g., 225° C., 235° C., 250° C. or 270° C. In someaspects, the channel temperature has an upper limit of 330° C., e.g.,325° C., 320° C., 315° C., 300° C., 290° C., or 280° C. In some aspects,the temperature may be raised within these ranges and limits to lowerthe RV of the product relative to the RV of the polyamide composition.In some aspects, the temperature may be lowered within these ranges andlimits to raise the RV of the product relative to the RV of thepolyamide composition.

Pressure

It has also been found that process pressures, such as the pressure ofthe pressurized gas used to extrude (spin) the polyamide into thenonwoven, may be tuned (optionally in combination with other parameters)to achieve the targeted (specific) nanofiber diameter and/or RV.

In one embodiment, the pressure may be tuned to achieve the desired endproduct nonwoven characteristic(s). For example, pressure may becontrolled to range from 150 kPa to 250 kPa, e.g., from 150 kPa to 240kPa, from 160 kPa to 220 kPa, from 170 kPa to 230 kPa, from 180 kPa to220 kPa, from 180 kPa to 215 kPa, from 190 kPa to 210 kPa, or from 182kPa to 218 kPa. In terms of lower limits, the pressure may be greaterthan 150 kPa, e.g., greater than 160 kPa, greater than 170 kPa, greaterthan 180 kPa, greater than 182 kPa, or greater than 190 kPa. In terms ofupper limits, the pressure may be less than 250 kPa, e.g., less than 240kPa, less than 230 kPa, less than 220 kPa, less than 218 kPa, less than215 kPa, or less than 210 kPa.

End Groups

In some aspects, the tunable aspect of the present disclosure allows formodifications to the polyamide composition in order to affect theproperties and/or characteristics of the resultant nanofibers and/ornonwoven product. For example, the polyamide composition may bemodified, during or subsequent to polymerization, to modify the ratio ofamine end groups to carboxylic acid end groups. Such a modification mayresult in unbalanced end groups. The ratio of diamine end groups tocarboxylic acid end groups may be adjusted within the range of 100:1 to1:100, e.g., 95:1 to 1:95, 75:1 to 1:75, 50:50, and all values inbetween. Without being bound by theory, it is believed that by havingunbalanced end groups, e.g., modifying the ratio of the end groups, theability to form acceptable products from a relatively low RV polyamidecomposition may be improved. Such a relatively low RV polyamidecomposition may have an RV from 2 to 30, e.g., from 2 to 25, from 2 to20, from 2 to 15, or from 2 to 10.

In an embodiment of the invention, advantages are envisioned having tworelated polymers with different RV values (both less than 330 and havingthe ability to form nanofibers with an average fiber diameter less than1 micron) blended for a desired property. For example, the melting pointof the polyamide may be increased, the RV adjusted, or other propertiesadjusted.

Catalyst

In some cases, a catalyst may be added in order to increase the reactionrate. The inclusion of a catalyst may affect the reaction kinetics, butnot the actual K value (reaction equilibrium constant value). Exemplarycatalysts include benzene phosphinic acid, benzene phosphonic acid,sodium hypophosite, hypophosphorus acid, monosodium phosphate,phosphoric acid, or combinations thereof. Without being bound by theory,it is postulated that the catalyst may be added to increase the reactionrate, achieving the desired RV and reducing the residence time in thespinning system. Such results may be advantageous by allowing the use oflower cost equipment to achieve a desired RV that is greater than theinitial polyamide composition.

Other Components

In some embodiments, the resultant nanofibers contain small amounts, ifany, of solvent. Accordingly, in some aspects, the resultant nanofibersare free of solvent. The use of the melt spinning process advantageouslyreduces or eliminates the need for solvents. This reduction/eliminationleads to beneficial effects such as environmental friendliness andreduced costs. Fibers formed via solution spinning processes, which areentirely different from melt spinning processes described herein,require such solvents. In one embodiment, the polyamide nanofibernonwoven is melt-blown and/or is free of solvent. In some embodiments,the nanofibers comprise less than 1 wt. % solvent, less than 5000 ppm,less than 2500 ppm, less than 2000 ppm, less than 1500 ppm, less than1000 ppm, less than 500 ppm, less than 400 ppm, less than 300 ppm, lessthan 200 ppm, less than 100 ppm, or less than a detectable amount ofsolvent including zero. Solvents may vary depending on the components ofthe polyamide but may include formic acid, sulfuric acid, toluene,benzene, chlorobenzene, xylene/chlorohexanone, decalin, paraffin oil,ortho dichlorobenzene, and other known solvents. In terms of ranges,when small amounts of solvent are included, the resultant nanofibers mayhave at least 1 ppm, at least 5 ppm, at least 10 ppm, at least 15 ppm,or at least 20 ppm solvent. In some aspects, non-volatile solvents, suchas formic acid, may remain in the product and may require an additionalextraction step. Such an additional extraction step may add toproduction costs. In some aspects, the amount of solvent included, ifany, may be adjusted to affect the RV of the polyamide compositionand/or the RV of the product

In other embodiments, the nanofibers may be entangled with a scrimwithout the use of adhesives. Accordingly, the nanofibers contain noadhesives.

In some cases, the nanofiber may be made of a polyamide material thatoptionally includes an additive. Examples of suitable additives includeoils (such as finishing oils, e.g., silicone oils), waxes, solvents(including formic acid as described herein), lubricants (e.g., paraffinoils, amide waxes, and stearates), stabilizers (e.g., photostabilizers,UV stabilizers, etc.), delusterants, antioxidants, colorants, pigments,and dyes. The additives may be present in a total amount of up to 49 wt.% of the nanofiber nonwoven product, e.g., up to 40 wt. %, up to 30 wt.%, up to 20 wt. %, up to 10 wt. %, up to 5 wt. %, up to 3 wt. %, or upto 1 wt. %. In terms of lower limits, the additives may be present inthe nanofiber product in an amount of at least 0.01 wt. %, e.g., atleast 0.05 wt. %, at least 0.1 wt. %, at least 0.25 wt. %, or at least0.5 wt. %. In terms of ranges, the additives may be present in thenanofiber product in an amount from 0.01 to 49 wt. %, e.g., from 0.05 to40 wt. %, from 0.1 to 30 wt. %, from 0.25 to 20 wt. %, from 0.5 to 10wt. %, from 0.5 to 5 wt. %, or from 0.5 to 1 wt. %. In some aspects,monomers and/or polymers may be included as additives. For example,nylon 6I and/or nylon 6T may be added as an additive. In some aspects,the presence and/or amount of additive included may be adjusted tomodify the RV of the polyamide composition and/or the product.

Antioxidants suitable for use in conjunction with the nanofiber nonwovenproduct described herein may, in some embodiments, include, but are notlimited to, anthocyanin, ascorbic acid, glutathione, lipoic acid, uricacid, resveratrol, flavonoids, carotenes (e.g., beta-carotene),carotenoids, tocopherols (e.g., alpha-tocopherol, beta-tocopherol,gamma-tocopherol, and delta-tocopherol), tocotrienols, ubiquinol, gallicacids, melatonin, secondary aromatic amines, benzofuranones, hinderedphenols, polyphenols, hindered amines, organophosphorus compounds,thioesters, benzoates, lactones, hydroxylamines, and the like, and anycombination thereof. In some embodiments, the antioxidant may beselected from the group consisting of stearyl3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate,bis(2,4-dicumylphenyl)pentaerythritol diphosphite,tris(2,4-di-tert-butylphenyl)phosphite, bisphenol A propoxylatediglycidyl ether, 9,10-dihydroxy-9-oxa-10-phosphaphenanthrene-10-oxideand mixtures thereof.

Colorants, pigments, and dyes suitable for use in conjunction with thenanofiber nonwoven product described herein may, in some embodiments,include, but are not limited to, plant dyes, vegetable dyes, titaniumdioxide (which may also act as a delusterant), carbon black, charcoal,silicon dioxide, tartrazine, E102, phthalocyanine blue, phthalocyaninegreen, quinacridones, perylene tetracarboxylic acid di-imides,dioxazines, perinones disazo pigments, anthraquinone pigments, metalpowders, iron oxide, ultramarine, nickel titanate, benzimidazoloneorange gl, solvent orange 60, orange dyes, calcium carbonate, kaolinclay, aluminum hydroxide, barium sulfate, zinc oxide, aluminum oxide,CARTASOL® dyes (cationic dyes, available from Clariant Services) inliquid and/or granular form (e.g., CARTASOL Brilliant Yellow K-6Gliquid, CARTASOL Yellow K-4GL liquid, CARTASOL Yellow K-GL liquid,CARTASOL Orange K-3GL liquid, CARTASOL Scarlet K-2GL liquid, CARTASOLRed K-3BN liquid, CARTASOL Blue K-5R liquid, CARTASOL Blue K-RL liquid,CARTASOL Turquoise K-RL liquid/granules, CARTASOL Brown K-BL liquid),FASTUSOL® dyes (an auxochrome, available from BASF) (e.g., Yellow 3GL,Fastusol C Blue 74L), and the like, any derivative thereof, and anycombination thereof. In some embodiments, solvent dyes may be employed.

Method of Forming the Nanofibers

As described herein, the nanofiber nonwoven product is formed byspinning or melt blowing to form a spun product. Spinning, as usedherein, refers to the steps of melting a polyamide composition andforming the polyamide composition into fibers. Examples of spinninginclude centrifugal spinning, melt blowing, spinning through a spinneret(e.g., a spinneret without a charge) or die, and “island-in-the sea”geometry. “Island-in-the-sea” refers to fibers forming by extruding atleast two polymer components from one spinning die, also referred to asconjugate or bicomponent spinning. As used herein, spinning specificallyexcludes solution spinning and electrospinning.

In some aspects, the polyamide nanofiber is melt blown. Melt blowing isadvantageously less expensive than electrospinning. Melt blowing is aprocess type developed for the formation of nanofibers and nonwovenwebs; the nanofibers are formed by extruding a molten thermoplasticpolymeric material, or polyamide, through a plurality of small holes.The resulting molten threads or filaments pass into converging highvelocity gas streams which attenuate or draw the filaments of moltenpolyamide to reduce their diameters. Thereafter, the melt blownnanofibers are carried by the high velocity gas stream and deposited ona collecting surface, or forming wire, to form a nonwoven web ofrandomly disbursed melt blown nanofibers. The formation of nanofibersand nonwoven webs by melt blowing is well known in the art. See, by wayof example, U.S. Pat. Nos. 3,016,599; 3,704,198; 3,755,527; 3,849,241;3,978,185; 4,100,324; 4,118,531; and 4,663,220.

An embodiment of making the inventive nanofiber nonwovens is by way of2-phase spinning or melt blowing with propellant gas through a spinningchannel as is described generally in U.S. Pat. No. 8,668,854. Thisprocess includes two phase flow of polymer or polymer solution and apressurized propellant gas (typically air) to a thin, preferablyconverging channel. The channel is usually and preferably annular inconfiguration. It is believed that the polymer is sheared by gas flowwithin the thin, preferably converging channel, creating polymeric filmlayers on both sides of the channel. These polymeric film layers arefurther sheared into nanofibers by the propellant gas flow. Here again,a moving collector belt may be used and the basis weight of thenanofiber nonwoven is controlled by regulating the speed of the belt.The distance of the collector may also be used to control fineness ofthe nanofiber nonwoven. The process is better understood with referenceto FIG. 1.

Additional methods and the associated equipment are disclosed in U.S.Pat. Nos. 7,300,272; 8,668,854; and 8, 658,067, described herein.Depending on the desired properties of the product, the equipment may bechosen accordingly. For example, such properties include RV, averagenanofiber diameter, nanofiber diameter distribution, air permeabilityvalue, TDI, and ODI. Each property and the desirable ranges for eachproperty are discussed further herein. In addition to adjusting theequipment used in the spinning process, the RV of the polyamidecomposition may also optionally be adjusted. The RV of the polyamidecomposition may be adjusted to achieve one of the properties describedabove. The equipment and RV may be selected to achieve the same propertyor they may independently be selected to achieve different properties.For example, the residence time and heat transfer of equipment may beadjusted to reduce the ODI and TDI of the nanofiber fabric. Differentmelt spinning equipment may also have different optimal RV ranges thatimpacts the capability to achieve the desired targeted properties of thenanofiber fabric. Beneficially, the use of the aforementioned polyamidecomposition in the melt spinning process provides for significantbenefits in production rate, e.g., at least 5% greater, at least 10%greater, at least 20% greater, at least 30% greater, at least 40%greater.

FIG. 1 illustrates schematically operation of a system for spinning ananofiber nonwoven including a polyamide feed assembly 110, an air feed1210 a spinning cylinder 130, a collector belt 140 and a take up reel150. During operation, polyamide melt or solution is fed to spinningcylinder 130 where it flows through a thin channel in the cylinder withhigh pressure air, shearing the polyamide into nanofibers. Details areprovided in the aforementioned U.S. Pat. No. 8,668,854. The throughputrate and basis weight is controlled by the speed of the belt.Optionally, functional additives such as charcoals, copper or the likecan be added with the air feed, if so desired.

In an alternate construction of the spinneret used in the system of FIG.1, particulate material may be added with a separate inlet as is seen inU.S. Pat. No. 8,808,594.

Still yet another methodology which may be employed is melt blowing thepolyamide nanofiber webs of the invention (FIG. 2). Melt blowinginvolves extruding the polyamide into a relatively high velocity,typically hot, gas stream. To produce suitable nanofibers, carefulselection of the orifice and capillary geometry as well as thetemperature is required as is seen in: Hassan et al., J Membrane Sci.,427, 336-344, 2013 and Ellison et al., Polymer, 48 (11), 3306-3316,2007, and, International Nonwoven Journal, Summer 2003, pg 21-28.

U.S. Pat. No. 7,300,272 discloses a fiber extrusion pack for extrudingmolten material to form an array of nanofibers that includes a number ofsplit distribution plates arranged in a stack such that each splitdistribution plate forms a layer within the fiber extrusion pack, andfeatures on the split distribution plates form a distribution networkthat delivers the molten material to orifices in the fiber extrusionpack. Each of the split distribution plates includes a set of platesegments with a gap disposed between adjacent plate segments. Adjacentedges of the plate segments are shaped to form reservoirs along the gap,and sealing plugs are disposed in the reservoirs to prevent the moltenmaterial from leaking from the gaps. The sealing plugs can be formed bythe molten material that leaks into the gap and collects and solidifiesin the reservoirs or by placing a plugging material in the reservoirs atpack assembly. This pack can be used to make nanofibers with a meltblowing system described in the patents previously mentioned.

The spinning processes described herein can form a polyamide nanofibernonwoven product having a relatively low oxidative degradation index(“ODI”) value. A lower ODI indicates less severe oxidative degradationduring manufacture. In some aspects, the ODI may range from 10 to 150ppm. ODI may be measured using gel permeation chromatography (GPC) witha fluorescence detector. The instrument is calibrated with a quinineexternal standard. 0.1 grams of nylon is dissolved in 10 mL of 90%formic acid. The solution is then analyzed by GPC with the fluorescencedetector. The detector wavelengths for ODI are 340 nm for excitation and415 nm for emission. In terms of upper limits, the ODI of the polyamidenanofiber nonwoven may be 200 ppm or less, e.g., 180 ppm or less, 150ppm or less, 125 ppm or less, 100 ppm or less, 75 ppm or less, 60 ppm orless, or 50 ppm or less. In terms of the lower limits, the ODI of thepolyamide nanofiber nonwoven may be 1 ppm or greater, 5 ppm or greater,10 ppm or greater, 15 ppm or greater, 20 ppm or greater, or 25 ppm orgreater. In terms of ranges, the ODI of the polyamide nanofiber nonwovenmay be from 1 to 200 ppm, from 1 to 180 ppm, from 1 to 150 ppm, from 5to 125 ppm, from 10 to 100 ppm, from 1 to 75 ppm, from 5 to 60 ppm, orfrom 5 to 50 ppm.

Additionally, the spinning processes as described herein can result in arelatively low thermal degradation index (“TDI”). A lower TDI indicatesa less severe thermal history of the polyamide during manufacture. TDIis measured the same as ODI, except that the detector wavelengths forTDI are 300 nm for excitation and 338 nm for emission. In terms of upperlimits, the TDI of the polyamide nanofiber nonwoven may be 4000 ppm orless, e.g., 3500 ppm or less, 3100 ppm or less, 2500 ppm or less, 2000ppm or less, 1000 ppm or less, 750 ppm or less, or 700 ppm or less. Interms of the lower limits, the TDI of the polyamide nanofiber nonwovenmay be 20 ppm or greater, 100 ppm or greater, 125 ppm or greater, 150ppm or greater, 175 ppm or greater, 200 ppm or greater, or 210 ppm orgreater. In terms of ranges, the TDI of the polyamide nanofiber nonwovenmay be from 20 to 4000 ppm, 100 to 4000 ppm, from 125 to 3500 ppm, from150 to 3100 ppm, from 175 to 2500 ppm, from 200 to 2000 ppm, from 210 to1000 ppm, from 200 to 750 ppm, or from 200 to 700 ppm.

TDI and ODI test methods are also disclosed in U.S. Pat. No. 5,411,710.Lower TDI and/or ODI values are beneficial because they indicate thatthe nanofiber nonwoven product is more durable than products havinggreater TDI and/or ODI. As explained above, TDI and ODI are measures ofdegradation and a product with greater degradation would not perform aswell. For example, such a product may have reduced dye uptake, lowerheat stability, lower life in a filtration application where the fibersare exposed to heat, pressure, oxygen, or any combination of these, andlower tenacity in industrial fiber applications. Although a low TDIand/or ODI may be preferable, the TDI and/or ODI values may be balancedwith other desirable properties disclosed herein, including averagenanofiber diameter, nanofiber diameter distribution, air permeabilityvalue, relative viscosity, mean pore flow diameter, and filtrationefficiency.

One possible method that may be used in forming a nanofiber nonwovenproduct with a lower TDI and/or ODI would be to include additives asdescribed herein, especially antioxidants. Such antioxidants, althoughnot necessary in conventional processes, may be used to inhibitdegradation. An example of useful antioxidants include copper halidesand Nylostab® S-EED® available from Clariant.

The spinning or melt blowing methods as described herein may also resultin a nanofiber nonwoven product having an Air Permeability Value of lessthan 600 CFM/ft², e.g., less than 590 CFM/ft², less than 580 CFM/ft²,less than 570 CFM/ft², less than 560 CFM/ft², or less than 550 CFM/ft².In terms of lower limits, the nanofiber nonwoven product may have an AirPermeability Value of at least 50 CFM/ft2, at least 75 CFM/ft2, at least100 CFM/ft², at least 125 CFM/ft², at least 150 CFM/ft², or at least 200CFM/ft². In terms of ranges, the nanofiber nonwoven product may have anAir Permeability Value from 50 to 600 CFM/ft², from 75 to 590 CFM/ft²,from 100 to 580 CFM/ft², from 125 to 570 CFM/ft², from 150 to 560CFM/ft², or from 200 to 550 CFM/ft².

The spinning methods as described herein may also result in a nanofibernonwoven product having a filtration efficiency, as measured by a TSI3160 or a TSI 8130 automated filter tester from 1 to 99.999%, e.g., from1 to 95%, from 1 to 90%, from 1.5 to 85%, or from 2 to 80%. The TSI 3160Automated Filter Tester is used to test the efficiency of filtermaterials. Particle penetration and pressure drop are the two importantparameters measured using this instrument. Efficiency is100%−penetration. A challenge solution with known particle size is used.The TSI 3160 is used to measure Hepa filters and uses a DOP solution. Itcombines an Electrostatic Classifier with dual Condensation ParticleCounters (CPCs) to measure most penetrating particle size (MPPS) from 15to 800 nm using monodisperse particles. And can test efficiencies up to99.999999%.

Applications

The inventive nanofiber nonwovens are useful in a variety ofapplications due to their high temperature resistance, barrier,permeability properties, and, processability. The products may be usedin multilayer structures including laminates in many cases.

Thus, the products are used in air or liquid filtration in the followingsectors: transportation; industrial; commercial and residential.

The products are likewise suitable for barrier applications inbreathable fabrics, surgical nonwovens, baby care, adult care, apparel,composites, construction and acoustics. The compositions are useful forsound dampening in automotive, electronic and aircraft applicationswhich may require composites of different fiber sizes for bestperformance. At higher basis weights, the products are used inconnection with beverages, food packaging, transportation, chemicalprocessing and medical applications such as wound dressings or medicalimplants.

The unique characteristics of the nonwovens of the invention providefunctionality and benefits not seen in conventional products, forexample, the nonwovens of the invention can be used as packaging forsmoked meats.

EMBODIMENTS Embodiment 1

A method of controlling the RV of a polyamide nanofiber nonwovenproduct, comprising: (a) providing a polyamide composition having an RVfrom 2 to 330 for spinning; (b) determining a desired RV for thepolyamide nanofiber nonwoven product; (c) selecting at least onecondition for the spinning selected from temperature, moisture content,and presence of a catalyst; (d) spinning or melt blowing the polyamidecomposition under the at least one condition into a plurality ofnanofibers; and (e) forming the nanofibers into the nanofiber nonwovenproduct, wherein the product has an average nanofiber diameter from 100to 1000 nanometers and an RV from 2 to 330.

Embodiment 2

The method according to Embodiment 1, wherein the temperature is from215° C. to 315° C.

Embodiment 3

The method according to Embodiment 1, wherein the moisture content isfrom 5 ppm to 5 wt. %.

Embodiment 4

The method according to Embodiment 1, wherein the desired RV of thepolyamide nanofiber nonwoven product is greater than the RV of thepolyamide composition.

Embodiment 5

The method according to Embodiment 4, wherein the temperature of thespinning step is adjusted to be within the range of 215° C. to 315° C.

Embodiment 6

The method according to Embodiment 4, wherein the moisture content isadjusted within the range of 5 ppm to 5 wt. %.

Embodiment 7

The method according to Embodiment 4, wherein the desired RV of theproduct is at least 10% greater than the RV of the polyamidecomposition.

Embodiment 8

The method according to Embodiment 1, wherein the desired RV of productis less than the RV of the polyamide composition.

Embodiment 9

The method according to Embodiment 9, wherein the temperature of thespinning step is increased within the range of 215° C. to 315° C.

Embodiment 10

The method according to Embodiment 9, wherein the moisture content isincreased within the range of 5 ppm to 5 wt. %.

Embodiment 11

The method according to Embodiment 9, wherein the desired RV of theproduct is at least 10% less than the RV of the polyamide composition.

Embodiment 12

The method according to any of the preceding Embodiments, wherein thecatalyst comprises benzene phosphinic acid, benzene phosphonic acid,sodium hypophosite, hypophosphorus acid, monosodium phosphate,phosphoric acid, or combinations thereof.

Embodiment 13

The method according to any of the preceding Embodiments, wherein thepolyamide composition comprises nylon 66 and/or nylon 6/66.

Embodiment 14

The method according to any of the preceding Embodiments, wherein themelt point of the product is 225° C. or greater.

Embodiment 15

The method according to any of the preceding Embodiments, wherein nomore than 20% of the nanofibers have a diameter of greater than 700nanometers.

Embodiment 16

The method according to any of the preceding Embodiments, wherein thepolyamide is a high temperature nylon.

Embodiment 17

The method according to any of the preceding Embodiments, wherein thepolyamide comprises N6, N66, N6T/66, N612, N6/66, N6I/66, N66/6I/6T,N11, and/or N12, wherein “N” means Nylon.

Embodiment 18

The method according to any of the preceding Embodiments, wherein theproduct has an Air Permeability Value of less than 600 CFM/ft².

Embodiment 19

The method according to any of the preceding Embodiments, wherein theproduct has a basis weight of 150 GSM or less.

Embodiment 20

The method according to any of the preceding Embodiments, wherein theproduct has a TDI of at least 20 ppm.

Embodiment 21

The method according to any of the preceding Embodiments, wherein theproduct has an ODI of at least 1 ppm.

Embodiment 22

The method according to any of the preceding Embodiments, wherein theproduct is free of solvent.

Embodiment 23

The method according to any of the preceding Embodiments, wherein theproduct comprises less than 5000 ppm solvent.

Embodiment 24

The method according to any of the preceding Embodiments, wherein thepolyamide composition is melt spun by way of melt-blowing through a dieinto a high velocity gaseous stream.

Embodiment 25

The method according to any of Embodiments 1-23, wherein the polyamidecomposition is melt-spun by 2-phase propellant-gas spinning, includingextruding the polyamide composition in liquid form with pressurized gasthrough a fiber-forming channel.

Embodiment 26

The method according to any of the preceding Embodiments, wherein thenanofiber nonwoven product is formed by collecting the nanofibers on amoving belt.

Embodiment 27

A method for preparing a polyamide nanofiber nonwoven product whereinfrom 1 to 20% of the nanofiber diameters are greater than 700nanometers, comprising: (a) providing a polyamide composition having anRV from 2 to 330 for spinning; (b) spinning or melt blowing thepolyamide composition at a temperature in the range of 215° C. to 315°C. into a plurality of nanofibers; and (c) forming the nanofibers intothe nanofiber nonwoven product, wherein the product has an RV from 2 to330.

Embodiment 28

The method according to Embodiment 27, wherein the polyamide compositionis spun through a die or capillary.

Embodiment 29

The method according to Embodiment 28, wherein the throughput rate ofthe polyamide composition through the die or capillary is adjustedwithout substantially changing the average nanofiber diameter and/or thenanofiber diameter distribution.

Embodiment 30

The method according to Embodiment 28, wherein a number of holes perinch of the die or capillary is adjusted to adjust the average nanofiberdiameter and/or the nanofiber diameter distribution.

Embodiment 31

The method according to Embodiment 28, wherein the size of the holes ofthe die or capillary is adjusted to adjust the average nanofiberdiameter and/or the nanofiber diameter distribution.

Embodiment 32

The method according to any of Embodiments 27-31, wherein the desired RVof the polyamide nanofiber product is at least 10% less than the RV ofthe polyamide composition.

Embodiment 33

The method according to any of Embodiments 27-32, wherein the method isoperated at a temperature from 215° C. to 315° C.

Embodiment 34

The method according to any of Embodiments 27-33, wherein the method isoperated at a moisture content from 5 ppm to 5 wt. %.

Embodiment 35

The method according to any of Embodiments 27-34, wherein the method isoperated in the presence of a catalyst comprising benzene phosphinicacid, benzene phosphonic acid, sodium hypophosite, hypophosphorus acid,monosodium phosphate, phosphoric acid, or combinations thereof.

Embodiment 36

The method according to any of Embodiments 27-35, wherein the polyamidecomposition comprises nylon 66 and/or nylon 6/66.

Embodiment 37

The method according to any of Embodiments 27-36, wherein the melt pointof the product is 225° C. or greater.

Embodiment 38

The method according to any of Embodiments 27-37, wherein no more than20% of the nanofibers have a diameter of greater than 700 nanometers.

Embodiment 39

The method according to any of Embodiments 27-38, wherein the polyamideis a high temperature nylon.

Embodiment 40

The method according to any of Embodiments 27-39, wherein the polyamidecomprises N6, N66, N6T/66, N612, N6/66, N6I/66, N66/6I/6T, N11, and/orN12, wherein “N” means Nylon.

Embodiment 41

The method according to any of Embodiments 27-40, wherein the producthas an Air Permeability Value of less than 600 CFM/ft².

Embodiment 42

The method according to any of Embodiments 27-41, wherein the producthas a basis weight of 150 GSM or less.

Embodiment 43

The method according to any of Embodiments 27-42, wherein the producthas a TDI of at least 20 ppm.

Embodiment 44

The method according to any of Embodiments 27-43, wherein the producthas an ODI of at least 1 ppm.

Embodiment 45

The method according to any of Embodiments 27-44, wherein the product isfree of solvent.

Embodiment 46

The method according to any of Embodiments 27-45, wherein the productcomprises less than 5000 ppm solvent.

Embodiment 47

The method according to any of the Embodiments 27-46, wherein thepolyamide composition is melt spun by way of melt-blowing through a dieinto a high velocity gaseous stream.

Embodiment 48

The method according to any of Embodiments 27-46, wherein the polyamidecomposition is melt-spun by 2-phase propellant-gas spinning, includingextruding the polyamide composition in liquid form with pressurized gasthrough a fiber-forming channel.

Embodiment 49

The method according to any of Embodiments 27-48, wherein the nanofibernonwoven product is formed by collecting the nanofibers on a movingbelt.

Embodiment 50

A method of manufacturing a polyamide nanofiber nonwoven product,comprising: (a) providing a polyamide composition having an RV from 2 to330 for spinning; (b) determining one or more desired properties for thepolyamide nanofiber nonwoven product, the properties comprising averagenanofiber diameter, nanofiber diameter distribution, air permeabilityvalue, TDI, ODI, relative viscosity, mean pore flow diameter, andfiltration efficiency; (c) selecting equipment to spin the polyamidecomposition to produce the polyamide nanofiber nonwoven product; (d)optionally adjusting the RV of the polyamide composition based upon atleast one of the desired properties of the polyamide nanofiber nonwovenproduct and the selected equipment; (e) spinning or melt blowing thepolyamide composition into a plurality of nanofibers at a temperature;and (f) forming the nanofibers into the nanofiber nonwoven product,wherein the product has an average nanofiber diameter from 100 to 1000nanometers and an RV from 2 to 330.

Embodiment 51

The method according to Embodiment 50, wherein the equipment comprises afiber extrusion pack including a number of split distribution platesarranged in a stack to form a distribution network.

Embodiment 52

The method according to Embodiment 50, wherein the equipment comprises atwo-phase flow nozzle and a converging channel; wherein the convergingchannel accelerates the polyamide composition from the two-phase flownozzle to a channel exit to form a polymeric film along the surface ofthe converging channel, wherein the polymeric film is fibrillated at thechannel exit to form the nanofibers; and collecting the nanofibers toform the product.

Embodiment 53

The method according to Embodiment 50, wherein the equipment comprises afiber producing device comprising a body configured to receive thepolyamide composition, a driver capable of rotating the body, adeposition system for directing nanofibers formed in the body toward asubstrate, and a substrate transfer system for moving substrate materialthrough a deposition system for directing the nanofibers to thesubstrate.

Embodiment 54

The method according to Embodiment 50, wherein the polyamide compositionis spun through a die or capillary.

Embodiment 55

The method according to Embodiment 54, wherein the throughput rate ofthe polyamide composition through the die or capillary is adjustedwithout substantially changing the average nanofiber diameter and/or thenanofiber diameter distribution.

Embodiment 56

The method according to Embodiment 54, wherein a number of holes perinch of the die or capillary is adjusted to adjust the average nanofiberdiameter and/or the nanofiber diameter distribution.

Embodiment 57

The method according to Embodiment 54, wherein the size of the holes ofthe die or capillary is adjusted to adjust the average nanofiberdiameter and/or the nanofiber diameter distribution.

Embodiment 58

The method according to any of Embodiments 50-57, wherein the desired RVof the polyamide nanofiber product is at least 10% less than the RV ofthe polyamide composition.

Embodiment 59

The method according to any of Embodiments 50-58, wherein the polyamidecomposition RV is adjusted by operating at a temperature from 215° C. to315° C.

Embodiment 60

The method according to any of Embodiments 50-59, wherein the polyamidecomposition RV is adjusted by operating at a moisture content from 5 ppmto 5 wt. %.

Embodiment 61

The method according to any of Embodiments 50-60, wherein the polyamidecomposition RV is adjusted by operating in the presence of a catalystcomprising benzene phosphinic acid, benzene phosphonic acid, sodiumhypophosite, hypophosphorus acid, monosodium phosphate, phosphoric acid,or combinations thereof.

Embodiment 62

The method according to any of Embodiments 50-61, wherein the polyamidecomposition comprises nylon 66 and/or nylon 6/66.

Embodiment 63

The method according to any of Embodiments 50-62, wherein the melt pointof the product is 225° C. or greater.

Embodiment 64

The method according to any of Embodiments 50-63, wherein no more than20% of the nanofibers have a diameter of greater than 700 nanometers.

Embodiment 65

The method according to any of Embodiments 50-64, wherein the polyamideis a high temperature nylon.

Embodiment 66

The method according to any of Embodiments 50-65, wherein the polyamidecomprises N6, N66, N6T/66, N612, N6/66, N6I/66, N66/6I/6T, N11, and/orN12, wherein “N” means Nylon.

Embodiment 67

The method according to any of Embodiments 50-66, wherein the producthas an Air Permeability Value of less than 600 CFM/ft².

Embodiment 68

The method according to any of Embodiments 50-67, wherein the producthas a basis weight of 150 GSM or less.

Embodiment 69

The method according to any of Embodiments 50-68, wherein the producthas a TDI of at least 20 ppm.

Embodiment 70

The method according to any of Embodiments 50-69, wherein the producthas an ODI of at least 1 ppm.

Embodiment 71

The method according to any of Embodiments 50-70, wherein the product isfree of solvent.

Embodiment 72

The method according to any of Embodiments 50-71, wherein the productcomprises less than 5000 ppm solvent.

Embodiment 73

The method according to any Embodiment 50, wherein the polyamidecomposition is melt spun by way of melt-blowing through a die into ahigh velocity gaseous stream.

Embodiment 74

The method according to Embodiment 50, wherein the polyamide compositionis melt-spun by 2-phase propellant-gas spinning, including extruding thepolyamide composition in liquid form with pressurized gas through afiber-forming channel.

Embodiment 75

The method according to Embodiment 50, wherein the nanofiber nonwovenproduct is formed by collecting the nanofibers on a moving belt.

Embodiment 76

The method according to Embodiment 50, wherein the RV of the polyamidecomposition is adjusted by adjusting the ratio of amine to carboxylicacid groups in the polyamide composition.

Embodiment 77

The method according to Embodiment 76, wherein the ratio of amine tocarboxylic acid end group in the polyamide composition is from 1:100 to100:1.

Embodiment 78

A method of manufacturing a polyamide nanofiber nonwoven product,comprising: (a) determining one or more desired properties for thepolyamide nanofiber nonwoven product, the properties comprising averagenanofiber diameter, nanofiber diameter distribution, air permeabilityvalue, TDI, ODI, relative viscosity, mean pore flow diameter, andfiltration efficiency; (b) selecting equipment to spin the polyamidecomposition to produce the polyamide nanofiber nonwoven product; (c)determining a preferred RV of the polyamide composition based upon atleast one of the desired properties of the polyamide nanofiber nonwovenproduct and the selected equipment; (d) providing a polyamidecomposition having the preferred RV, wherein the RV of the polyamidecomposition is adjusted during or subsequent to polymerization of thepolyamide composition; (e) spinning or melt blowing the polyamidecomposition into a plurality of nanofibers at a temperature; and (f)forming the nanofibers into the nanofiber nonwoven product, wherein theproduct has the desired properties.

Embodiment 79

The method according to Embodiment 78, wherein the preferred RV of thepolyamide composition is from 2 to 330.

Embodiment 80

The method according to Embodiment 78, wherein the nanofiber nonwovenproduct has an RV from 2 to 330.

Embodiment 81

The method according to Embodiment 78, wherein the RV of the polyamidecomposition is adjusted by adjusting the ratio of amine to carboxylicacid groups in the polyamide composition.

Embodiment 82

The method according to Embodiment 81, wherein the ratio of amine tocarboxylic acid end group in the polyamide composition is from 100:1 to1:100.

Embodiment 83

The method according to Embodiment 78, wherein the polyamide compositionis spun through a die or capillary.

Embodiment 84

The method according to Embodiment 83, wherein a throughput rate of thepolyamide composition through the die or capillary is adjusted withoutsubstantially changing the average nanofiber diameter and/or thenanofiber diameter distribution.

Embodiment 85

The method according to Embodiment 83, wherein a number of holes perinch of the die or capillary is adjusted to adjust the average nanofiberdiameter and/or the nanofiber diameter distribution.

Embodiment 86

The method according to Embodiment 83, wherein the size of the holes ofthe die or capillary is adjusted to adjust the average nanofiberdiameter and/or the nanofiber diameter distribution.

Embodiment 87

The method according to any of Embodiments 81-86, wherein the RV of thepolyamide nanofiber product is at least 10% less than the RV of thepolyamide composition.

Embodiment 88

The method according to any of Embodiments 81-87, wherein the polyamidecomposition RV is adjusted by operating at a temperature from 215° C. to315° C.

Embodiment 89

The method according to any of Embodiments 81-88, wherein the polyamidecomposition RV is adjusted by operating at a moisture content from 5 ppmto 5 wt. %.

Embodiment 90

The method according to any of Embodiments 81-89, wherein the polyamidecomposition RV is adjusted by operating in the presence of a catalystcomprising benzene phosphinic acid, benzene phosphonic acid, sodiumhypophosite, hypophosphorus acid, monosodium phosphate, phosphoric acid,or combinations thereof.

Embodiment 91

The method according to any of Embodiments 81-90, wherein the polyamidecomposition comprises nylon 66 and/or nylon 6/66.

Embodiment 92

The method according to any of Embodiments 81-91, wherein the melt pointof the product is 225° C. or greater.

Embodiment 93

The method according to any of Embodiments 81-92, wherein no more than20% of the nanofibers have a diameter of greater than 700 nanometers.

Embodiment 94

The method according to any of Embodiments 81-93, wherein the polyamidecomposition is a high temperature nylon.

Embodiment 95

The method according to any of Embodiments 81-94, wherein the polyamidecomposition comprises N6, N66, N6T/66, N612, N6/66, N6I/66, N66/6I/6T,N11, and/or N12, wherein “N” means Nylon.

Embodiment 96

The method according to any of Embodiments 81-95, wherein the producthas an Air Permeability Value of less than 600 CFM/ft².

Embodiment 97

The method according to any of Embodiments 81-96, wherein the producthas a basis weight of 150 GSM or less.

Embodiment 98

The method according to any of Embodiments 81-97, wherein the producthas a TDI of at least 20 ppm.

Embodiment 99

The method according to any of Embodiments 81-98, wherein the producthas an ODI of at least 1 ppm.

Embodiment 100

The method according to any of Embodiments 81-99, wherein the product isfree of solvent.

Embodiment 101

The method according to any of Embodiments 81-100, wherein the productcomprises less than 5000 ppm solvent.

Embodiment 102

The method according to any of the Embodiments 81-101, wherein thepolyamide composition is melt spun by way of melt-blowing through a dieinto a high velocity gaseous stream.

Embodiment 103

The method according to any of Embodiments 81-102, wherein the polyamidecomposition is melt-spun by 2-phase propellant-gas spinning, includingextruding the polyamide composition in liquid form with pressurized gasthrough a fiber-forming channel.

Embodiment 104

The method according to any of Embodiments 81-103, wherein the nanofibernonwoven product is formed by collecting the nanofibers on a movingbelt.

Embodiment 105

The method according to Embodiment 78, wherein the equipment comprises afiber extrusion pack including a number of split distribution platesarranged in a stack to form a distribution network.

Embodiment 106

The method according to Embodiment 78, wherein the equipment comprises atwo-phase flow nozzle and a converging channel, wherein the convergingchannel accelerates the polyamide composition from the two-phase flownozzle to a channel exit to form a polymeric film along the surface ofthe converging channel, wherein the polymeric film is fibrillated at thechannel exit to form the nanofibers; and collecting the nanofibers toform the product.

Embodiment 107

The method according to Embodiment 78, wherein the equipment comprises afiber producing device comprising a body configured to receive thepolyamide composition, a driver capable of rotating the body, adeposition system for directing nanofibers formed in the body toward asubstrate, and a substrate transfer system for moving substrate materialthrough a deposition system for directing the nanofibers to thesubstrate.

Embodiment 108

A method of manufacturing a polyamide nanofiber nonwoven product,comprising: (a) providing a polyamide composition having an initial RVfor spinning; (b) determining one or more desired properties for thepolyamide nanofiber nonwoven product, the properties comprising averagenanofiber diameter, nanofiber diameter distribution, air permeabilityvalue, TDI, ODI, relative viscosity, mean pore flow diameter, andfiltration efficiency; (c) adjusting the initial RV of the polyamidecomposition based upon at least one of the desired properties to providean adjusted polyamide composition; (d) spinning or melt blowing theadjusted polyamide composition into a plurality of nanofibers at atemperature; and (f) forming the nanofibers into the nanofiber nonwovenproduct, wherein the product has an average nanofiber diameter from 100to 1000 nanometers and an RV from 2 to 330.

Embodiment 109

The process of Embodiment 108, wherein the adjusting is based on atleast one condition for the spinning, the condition comprisingtemperature, moisture content, and presence of a catalyst.

Embodiment 110

A method of manufacturing a polyamide nanofiber nonwoven product,comprising: (a) determining at least one desired property for thepolyamide nanofiber nonwoven product, the at least one desired propertycomprising average nanofiber diameter, nanofiber diameter distribution,air permeability value, TDI, ODI, relative viscosity, mean pore flowdiameter, and filtration efficiency; (c) determining at least onecondition to form the product with the desired at least one property;(d) spinning or melt blowing the polyamide composition into a pluralityof nanofibers at a temperature; and (e) forming the nanofibers into thenanofiber nonwoven product, wherein the product has the at least onedesired property.

Embodiment 111

The method according to Embodiment 110, wherein the at least onecondition is the type of equipment.

Embodiment 112

The method according to Embodiment 110, wherein the at least onecondition is the RV of the polyamide composition.

Embodiment 113

A method for tuning characteristics of a polyamide nanofiber nonwovencomprising the steps of targeting a specific average nanofiber diameterand/or a specific relative viscosity for the polyamide nanofibernonwoven, wherein the specific average nanofiber diameter is within arange from 100 nm to 1000 nm and/or the specific relative viscosity iswithin a range from 5 to 75 from 15 to 50 or from 20 to 40, extruding apolyamide composition having a moisture content with a pressurized gasthrough a fiber forming channel having a channel temperature to form thepolyamide nanofiber nonwoven having the target average nanofiberdiameter and/or relative viscosity, and controlling the moisturecontent, the pressure of pressurized gas, and/or the channel temperaturebased on the specific average nanofiber diameter and/or the specificrelative viscosity.

Embodiment 114

The method of Embodiment 113, wherein the specific average nanofiberdiameter is within a range of 200 nm to 700 nm.

Embodiment 115

The method of Embodiment 113, wherein the specific relative viscosity iswithin a range from 15 to 50 or from 20 to 40.

Embodiment 116

The method of Embodiment 113, wherein the moisture content is controlledfrom 0.005 wt. % to 1 wt. %, e.g., from 0.005 wt. % to 0.5 wt. %.

Embodiment 117

The method of Embodiment 113, wherein the moisture content is controlledby drying the polyamide composition to have a moisture content of lessthan 0.02 wt. %, and rehydrating the dried polyamide composition.

Embodiment 118

The method of Embodiment 113, wherein the pressure of the pressurizedgas is controlled to range from 160 kPa to 220 kPa.

Embodiment 119

The method of Embodiment 113, wherein the channel temperature iscontrolled to range from 270° C. to 330° C.

Embodiment 120

The method of Embodiment 113, wherein the fiber forming channelcomprises a die and/or a capillary.

Embodiment 121

The method of Embodiment 113, wherein the polyamide nanofiber nonwovenis melt-blown and/or is free of solvent.

Embodiment 122

The method of Embodiment 113, wherein the polyamide compositioncomprises a catalyst.

Embodiment 123

A method for tuning the relative viscosity of a polyamide nanofibernonwoven comprising the steps of targeting a specific relative viscosityfor the polyamide nanofiber nonwoven, wherein the specific relativeviscosity is within a range from 5 to 75, extruding a polyamidecomposition having a moisture content to form the polyamide nanofibernonwoven having the target relative viscosity, and controlling themoisture content based on the target relative viscosity.

Embodiment 124

The method of Embodiment 123, wherein the relative viscosity is targetedto a targeted relative viscosity within the range from 15 to 50 or from20 to 40.

Embodiment 125

The method of Embodiment 123, wherein the moisture content is controlledto range from 0.005 wt. % to 1 wt. %, e.g., from 0.005 wt. % to 0.5 wt.%.

Embodiment 126

The method of Embodiment 123, wherein the moisture content is controlledto range from 0.02 wt. % to 0.3 wt. %.

Embodiment 127

The method of Embodiment 123, wherein the controlling comprises dryingthe polyamide composition to have a moisture content of less than 0.02wt. %, and rehydrating the dried polyamide composition.

Embodiment 128

The method of Embodiment 123, wherein the polyamide composition isextruded through a fiber forming channel having a channel temperatureand the channel temperature is controlled to range from 270° C. to 330°C.

Embodiment 129

The method of Embodiment 123, wherein the polyamide nanofiber nonwovenis melt-blown and/or is free of solvent.

Embodiment 130

The method of Embodiment 123, wherein the polyamide compositioncomprises a catalyst.

Embodiment 131

A method for tuning the nanofiber diameter of a polyamide nanofibernonwoven comprising the steps of targeting a specific average nanofiberdiameter, wherein the specific average nanofiber diameter is within arange from 100 nm to 1000 nm, extruding a polyamide composition with apressurized gas to form the polyamide nanofiber nonwoven having thetarget average nanofiber diameter, and controlling the pressure of thepressurized gas based on the target average nanofiber diameter.

Embodiment 132

The method of Embodiment 131, wherein the fiber diameter is targeted toa target average nanofiber diameter within the range of 200 nm to 700nm.

Embodiment 133

The method of Embodiment 131, wherein the pressurized gas is controlledto range from 160 kPa to 220 kPa.

Embodiment 134

The method of Embodiment 131, wherein the polyamide composition isextruded through a fiber forming channel having a channel temperatureand the channel temperature is controlled to range from 270° C. to 330°C.

Embodiment 135

The method of Embodiment 131, wherein the polyamide composition has amoisture content and the moisture content is controlled to range from0.005 wt. % to 1 wt. %, e.g., from 0.005 wt. % to 0.5 wt. %.

Embodiment 136

The method of Embodiment 131, wherein the polyamide nanofiber nonwovenis melt-blown and/or is free of solvent.

The present disclosure is further understood by the followingnon-limiting examples.

EXAMPLES Example 1—Product RV and Average Fiber Diameter Tuned Based onMoisture Content

Low TDI/ODI (and a similar or slightly higher RV from polyamide toproduct) were selected as desired target product parameters. Thestarting RV of the polyamide composition was 7.3. Utilizing the meltspin procedures and apparatus as described in U.S. Pat. No. 8,668,854(shown generally in FIG. 1), Nylon 66 was spun onto a moving drum toproduce nonwoven webs. For this example, the targeted specific RV was 10and to achieve the specific RV, a moisture content of 0.28 wt. % wasused. A target specific fiber diameter range of 400 to 700 nm wasselected.

The process employed an extruder with a high compression screw,operating at 20 RPM. The screw temperature profile was tuned to reflectsteps of 245° C., 255° C., 265° C., and 265° C. The (precursor)polyamide temperature was tuned to 252° C. and nitrogen was used as thegas. Two nonwoven webs were produced (Samples 1 and 2), each havingdifferent basis weights. Sample 2 with the higher basis weight was madeby the same process, but the nanofibers were spun onto a scrim. In thisinstance, the scrim was merely used for adding integrity to theinventive nanofiber web. The RV of the polyamide was set at or adjustedto 7.3 (before spinning). To reduce the sensitivity of the relativeviscosity of the low RV polyamide to moisture content, to, the polyamidewas prepared using an excess of about 5% adipic acid.

The nonwoven webs were characterized for average fiber diameter, basisweight, air permeability in accordance with the Hassan et al. articlenoted above. Water vapor transmission rate was also measured (g/m²/24hr) according to ASTM E96, Procedure B (2016).

The results are shown in Table 1, and the nonwoven mats are shown in thephotomicrographs of FIGS. 3 and 4. The nanofibers of the nonwoven matshad an average fiber diameter ranging from 470 nm to 680 nm (575 nmaverage).

TABLE 1 Example 1: Precursor Polyamide and Product Properties FiberBasis Air PA diameter, weight, permeability WVTR Sample RV nm GSM(CFM/ft²) g/m²/24 hr TDI ODI Final RV 1 7.3 680 68 182.8 1140 56 12 10 27.3 470 118 182.8 1056 48 8 9.9

Thus, the results in Table 1 demonstrate that moisture content can betuned to achieve the targeted specific product RV and specific averagenanofiber diameter. For example, the use of these moisture contentsprovided for a melt spun nanofiber nonwoven web, the nanofibers of whichhad a fiber diameter averaging 570 for the initial RV of 7.3. Further,TDI and ODI numbers were surprisingly low and product RV was slightlyhigher than initial RV. Air Permeability was about 182.8 CFM/ft², whilewater vapor transmission rate averaged about 1100 g/m²/24 hrs. Suchfiber diameters and performance characteristics have not been achievedusing conventional polyamide precursors and/or processes. It is believedthat utilizing/tuning the RV of the resin and/or the temperature profileand/or nitrogen and/or moisture content are the main reasons for thesuperior TDI and ODI results and/or the final RV being similar orslightly higher than the initial RV.

Example 2—Product RV and Fiber Diameter Tuned Based on Moisture Contentand Channel Temperature

The moisture content and channel temperature (die temperature) weretuned to provide desired basis weight, air permeability, fiber diameter,product RV filtration efficiency, mean pore size pressure, mean poresize diameter, and other features, as shown below. Nylon 66 polyamidehaving an RV of 36 was melt spun and pumped to melt blown dies(utilizing the melt spin pack described in U.S. Pat. No. 7,300,272 andillustrated in FIG. 5) to produce nonwoven nanofiber webs. In thevarious samples, the moisture levels of nylon 66 ranged from about 0.2wt. % to about 0.3 wt. %. An extruder with three zones was used, and theextruder operated at temperatures ranging from 233° C. to 310° C. Thedie temperature ranged from 286° C. to 318° C. Heated air was used asthe gas. The nanofibers were deposited onto a 10 gsm thermally bonded,nylon spunbond scrim commercially available from Cerex Advanced Fabrics,Inc. under the trademark PBN-II®. Of course, other spunbond fabrics canbe used, for example, a polyester spun bond fabric, a polypropylenespunbond fabric, a nylon melt blown fabric or other woven, knit,needlepunched, or other nonwoven fabrics. No solvents or adhesives wereused during the melt spinning or deposition processes.

Various fabrics were made with webs of nanofibers. The properties andperformance characteristics of several specific samples are summarizedin Table 2.

TABLE 2 Example 2: Precursor Polyamide and Product Properties MeanAverage Nanofiber Mean pore Fiber Basis layer Air pore size sizeFiltration Product diameter, weight, thickness permeability diameterpressure Efficiency Sample RV (microns) (gsm) (microns) (CFM/ft²)(microns) (PSI) (%) 3 27.5 0.374 3.0 N/A 187 10.1 0.653 24.69 4 25.20.595 21.2 N/A 21.9 5.0 1.320 76.70 5 28.3 0.477 1.0 N/A 1002 84.1 0.812.71 6 22.9 0.577 2.8 44.8 354 20.0 0.358 10.38 7 24.1 0.601 7.3 60 75.77.2 0.919 40.68 8 23.9 0.490 10.1 88 52.9 5.9 1.121 53 9 23.5 0.53 13.2101.5 31.5 5.4 1.235 66.00

As indicated in Table 2, the disclosed process surprisingly yieldsnanofibers and nonwoven mats having synergistic combinations offeatures, e.g., RV and fiber diameter. The nanofiber nonwoven mats weresuccessfully made using the above described process, in various basisweights with a wide range of properties. Process settings can beadjusted to provide nanofiber fabrics with a variety of properties asrequired for the application as illustrated in Table 2.

Example 3—Product RV and Fiber Diameter Tuned Based on Moisture Contentand Channel Temperature

The moisture content and channel temperature of the following processwere tuned to reduce the RV of the fabric as compared to the startingpolyamide composition. A nylon 66 polyamide composition with an RV inthe range of about 34 to 37 was used with the pack described in U.S.Pat. No. 7,300,272 to make nanofibers with an RV of about 16.8. This isa reduction in RV from polyamide composition to fabric of about 17.2 to20.2 RV. The polyamide composition contained about 1 wt. % moisture andwas run on a small extruder with three zones ranging in temperature from233 to 310° C. A die temperature of about 308° C. was used. No solventsor adhesives were used during the melt spinning or deposition processes.

Example 4—Product RV and Fiber Diameter Tuned Based on Moisture Contentand Channel Temperature

The moisture content and channel temperature of the following processwere tuned to reduce the RV of the fabric as compared to the startingpolyamide composition. A nylon 66 polyamide composition with an RV inthe range of about 34 to 37 with the pack described in U.S. Pat. No.7,300,272 to make nanofibers with an RV of about 19.7. This is areduction in RV from polyamide composition to fabric of about 14.3 to17.3 RV units. The polyamide composition had a moisture content of 1 wt.% and was run on a small extruder with three zones ranging intemperature from 233 to 310° C. A die temperature of about 277° C. wasused. No solvents or adhesives were used during the melt spinning ordeposition processes. As shown, by lowering the temperature relative tothat used in Example 3, the product RV was greater than in Example 3with the same moisture content.

Example 5—Product RV and Fiber Diameter Tuned Based on Moisture Contentand Channel Temperature

The components of the polyamide composition, channel temperature, andmoisture content were tuned to adjust the RV of the product as comparedto Examples 3 and 4. A nylon 66 polyamide composition with an RV in therange of about 34 to 37 was used with 2% nylon 6 blended in. The packdescribed in U.S. Pat. No. 7,300,272 was used to make nanofibers with anRV of about 17.1. This is a reduction in RV from polyamide compositionto fabric of about 16.9 to 19.9 RV units. The polyamide composition hada moisture content of 1 wt. % and was run on a small extruder with threezones ranging in temperature from 233 to 310° C. A die temperature ofabout 308° C. was used. No solvents or adhesives were used during themelt spinning or deposition processes.

Example 6 Product RV and Fiber Diameter Tuned Based on Moisture Content

Seven polyamide compositions with varied RV's were provided as shownbelow in Table 3. The components of the polyamide, the polyamidecomposition RV, and the moisture content were tuned to form the producthaving the targeted RV, fiber diameter, ODI and TDI values shown below.The pack described in U.S. Pat. No. 7,300,272 was used to makenanofibers with RV values as reported below. Samples were made on asmall single screw extruder with a high residence time. Initially,Samples 10 and 11 were made by feeding more than enough chips into thefeed hopper of the extruder, the so-called “flood feeding” scheme. Inorder to reduce the transition time between items, the extruder and die(or pack) were starved of polyamide composition after Sample 11. Thisexample shows that a wide variety of nylon copolymers can be used tomake nylon nanofibers with fiber diameters in the 0.53 to 0.68 micronrange. Fiber diameters may be changed by changing process parameters,polymer formulations, or polymer types (copolymers). Based on the waythe samples were created, it is difficult to draw conclusions on thedegradation indices of these fabrics other than Samples 10 and 11.Samples 10 and 11 indicate that the addition of nylon 6 decreased thethermal degradation of the final nanofiber fabric. Comparing thesesamples to sample 16 also shows that adding nylon 6 decreases the fiberdiameter. Sample 13 shows that the RV was reduced from 303.1 to 33.3.This is a reduction of 269.8 units or an 89% reduction in RV.

TABLE 3 Example 6: Precursor Polyamide and Product Properties % FiberPolyamide Nylon Moisture Diameter Product ODI TDI Sample Components RV6, 6 (%) (microns) RV (ppm) (ppm) 10 Nylon 66/nylon 6 39.2 16 0.0810.531 29.7 75 798 11 Nylon 66/nylon 6 33.0 23 0.077 0.540 35.9 142 16912 Nylon 66 124 100 0.035 0.588 39.1 182 1613 13 Nylon 66 303 100 0.0180.638 33.3 208 1792 14 Nylon 66/nylon 6I 43.6 85 0.087 0.588 26.1 1722232 15 Nylon 66/nylon 6T 44.8 65 0.042 N/A N/A 224 2383 16 Nylon 66 36100 0.022 0.684 15.2 1430 >4000

Example 7—Tuning Based on Moisture Content and Channel Temperature

The channel temperature and equipment residence time were tuned to studythe effect on ODI and TDI. The moisture content and basis weight werealso tuned. The same nylon 66 polyamide composition with an RV in therange of about 34 to 37 that was used in example 3 was run in each ofthese samples. These samples were made on a slightly larger extruder anda much larger die (pack) with a much smaller residence time than thosein Table 3 with the same polyamide composition as that used to makesample 16. The die temperature, basis weight, and moisture content werevaried. Table 4 below shows the conditions and results. The results arealso shown in the graphs in FIGS. 7 and 8. As shown in Table 4 below,changing process variables does not dramatically change the ODI,illustrating a robust process for oxidative degradation. As shown inFIG. 8, as the meter pump speed decreased, the ODI and TDI generallyincreased with the TDI increasing at a higher percentage than the ODI.When compared to Sample 16 in Table 3, these samples show that the ODIand the TDI was lowered as this equipment used to run the nanofibernonwoven fabric was designed for a lower residence time.

TABLE 4 Example 7: TDI and ODI Values Die Moisture Basis Temp. MeterPump TDI ODI Sample (wt. %) Weight (° C.) Speed (rpm) (ppm) (ppm) 16 0.213.2 299 5.37 745 66 17 0.2 18.4 292 5.37 608 47 18 0.3 3.7 297 8.05 57259 19 0.2 3.2 297 8.05 676 59 20 0.2 6.2 297 10.73 214 34 21 0.2 11 29710.73 364 33 22 0.2 11 297 10.73 333 45 23 0.2 4.4 287 8.05 398 33 240.2 6.1 286 10.73 354 26 25 0.2 8 286 8.05 492 39 26 0.3 4.1 287 8.05464 32 27 0.3 6 300 10.73 433 28 28 0.3 6 289 10.73 441 40

Example 8 Tuning Based on Moisture Content

The moisture level and the basis weight were tuned to study their effecton pressure drop. Nylon 66 polyamide having an RV of 36 was melt spunand pumped to melt blown dies (utilizing the melt spin pack described inU.S. Pat. No. 7,300,272 and illustrated in FIG. 5) to produce nonwovennanofiber webs. The moisture level of nylon 66 was about 0.22 wt. %. Anextruder with three zones was used, and the extruder operated attemperatures ranging from 233° C. to 310° C. The channel temperature was295° C. Heated air was used as the gas. The nanofibers were depositedonto a 10 gsm thermally bonded, nylon spunbond scrim commerciallyavailable from Cerex Advanced Fabrics, Inc. under the trademark PBN-II®.Of course, other spunbond fabrics can be used, for example, a polyesterspun bond fabric, a polypropylene spunbond fabric, a nylon melt blownfabric or other woven, knit, needlepunched, or other nonwoven fabrics.No solvents or adhesives were used during the melt spinning ordeposition processes, and neither the polyamide or the resultant productcontained solvent or adhesive. The collector belt speed was set to makea fabric with a nylon 6,6 nanofiber layer of 82 gsm basis weight. Thisfabric had an efficiency of 97.9%, a pressure drop of 166.9 Pascals anda penetration of 2.1% as measured using the TSI 3160 previouslydiscussed. This fabric had a mean flow pore diameter average of 5.8microns with a range from 3.2 to 8 microns. The air permeability of thisfabric was 8.17 cfm/square foot. The thickness of the nanofiber layerwas 625 microns. The fabric were with the targeted RV and fiber diameterranges disclosed herein.

Example 9—Product RV Tuned Based on Moisture Content

Nonwovens were produced using a Nylon 6,6 polyamide composition as thestarting resin. The moisture content of the Nylon 6,6 polyamidecomposition ranged from 0.25 to 0.6 wt. %. The starting RV of thepolyamide composition was from about 34.4 to 37.7. In this example, themoisture level was tuned to study its effect on relative viscosity ofthe nonwoven, which was targeted to be 20 to 40. Fiber diameter wastargeted to be from 350 to 700 nm. The results are listed in Table 5 andshown in the chart in FIG. 9.

TABLE 5 Product RV Based on Moisture Moisture Air Pressure FiberDiameter Sample (wt. %) Product RV (kPa) (nm) 31 0.02 38.7 204.8 680 320.028 35.6 184.1 540 33 0.036 39.0 204.8 650 34 0.04 31.1 211.6 570 350.1 25.9 195.1 390 36 0.2 27.4 215.1 — 37 0.3 26.4 193.0 550 38 0.3225.9 187.5 360

The results show that by tuning the moisture content of the Nylon 6,6polyamide, the desired target fiber diameter and RV can be achieved.

Example 10—Product RV Tuned Based on Moisture Content & ChannelTemperature

Nonwovens were produced using a Nylon 6,6 polyamide composition as thestarting resin. The moisture content of the Nylon 6,6 polyamidecomposition ranged from 0.25 to 0.6 wt. %. The starting RV of thepolyamide composition was from about 34.4 to 37.7. The polyamidecomposition moisture and the channel temperature (die temperature) weretuned to arrive at specific relative viscosity (20 to 40) and/orspecific nanofiber diameter (350 to 700 nm). The nanofibers wereproduced by a meltblown process and were free of solvent. The averageresults are listed in Table 6 and the tuning based on moisture contentand channel temperatures is shown by FIG. 10. The RV of the nonwovenproduct can be tuned by adjusting the polyamide composition moisture andthe channel temperature. This shows that tuning the moisture content haslarger effect on the RV of the nonwoven product as compared with tuningthe channel temperature, although both effects are significant.

For example, at a polyamide composition moisture of 0.02 wt. % and a dietemperature of 306° C., the RV of the nonwoven product was 38.7.Increasing the resin moisture to 0.3 wt. % and decreasing the dietemperature slightly to 304° C. decreases the RV to 25.2. Similarly, ata polyamide composition moisture of 0.3 wt. % and a die temperature of301, an RV of 25.9 was measured. Decreasing the polyamide compositionmoisture to 0.1 wt. % increased the RV to 26.1.

TABLE 6 Tuning RV Based on Moisture Content and Channel TemperaturesChannel Air Nanofiber PA Moisture Temperature Pressure Diameter Sample(wt. %) (° C.) Product RV (kPa) (nm) 39 0.02 306 38.7 204.8 680 40 0.1301 26.1 197.9 — 41 0.1 307 28.1 184.1 390 42 0.1 310 25.7 197.9 — 430.1 312 25.5 197.9 — 44 0.1 314 25.4 197.9 450 45 0.1 315 25.1 197.9 38046 0.1 322 24.4 199.9 — 47 0.1 323 25.6 197.9 360 48 0.3 281 29.5 199.2660 49 0.3 283 28.9 170.3 560 50 0.3 284 27.8 181.3 620 51 0.3 285 26.5188.2 650 52 0.3 286 28.9 191.6 540 53 0.3 291 26.8 182.7 560 54 0.3 29227.1 177.2 540 55 0.3 294 26.1 184.1 680 56 0.3 297 25.2 186.1 440 570.3 298 22.6 184.1 570 58 0.3 299 25.8 184.1 520 59 0.3 300 26.2 194.4490 60 0.3 301 25.9 204.7 480 61 0.3 302 24.9 208.2 450 62 0.3 304 25.2228.9 — 63 0.3 311 23.3 — 460

The results in Table 6 show the advantages of tuning a characteristic bycontrolling the moisture content and channel temperature. This allows aprocesses to obtain different nonwoven products that are made from amelt-blown process.

Example 11—Fiber Diameter Tuned Based on Air Pressure & ChannelTemperature

The air pressure and the channel temperature, in particular dietemperature, were tuned and the fiber diameter was measured. The resultsare listed in Table 7, and shown in FIG. 11. Fiber diameter was targetedto be from 300 to 850 nm, with lower diameters (˜400 nm) beingparticularly desired. The fiber diameter of the fabric can be tuned byadjusting the air pressure and the die temperature. For example, at anair pressure of 184.1 kPa (12 psig) and a die temperature of 296° C.,the fiber diameter of the fabric was 475 nm. Increasing the air pressureto 190.9 kPa (13 psig) and increasing the die temperature to 297° C.decreased the fiber diameter to 402 nm. A combination of air pressureand die temperature can be selected to yield a specific fiber diameterwithin a typical amount of experimental and/or sampling variability.

TABLE 7 Tuning Pressure and Die Temperature Air Pressure Die TemperatureFiber diameter Sample (kPa) (° C.) (nm) 64 184.1 283 612 65 184.1 284805 66 184.1 285 669 67 184.1 291 580 68 184.1 294 647 69 184.1 296 47570 184.1 300 540 71 184.1 303 368 72 184.1 304 540 73 190.9 295 456 74190.9 296 516 75 190.9 297 402 76 190.9 298 512 77 190.9 307 349

Example 12—Product RV Tuned Based on Catalyst and Moisture Content

The RV of the nonwoven was tuned by adding a catalyst and setting themoisture at a specific level.

For example, a polyamide 6,6 resin with 150 ppm P can be used to makenanofiber nonwoven fabric using the melt blowing apparatus described inthe specification.

A polyamide 6,6 resin that contains this level of phosphorous iscommercially available from Ascend Performance Materials under theproduct type 42 AK2. The initial RV of the resin is 42. The final fabricRV would be estimated to be around 30 when the resin is dried to about0.3%. The final fabric RV would be estimated around 44 if the resin wasdried to about 0.05%.

While the disclosure has been described in detail, modifications withinthe spirit and scope of the disclosure will be readily apparent to thoseof skill in the art. Such modifications are also to be considered aspart of the present disclosure. In view of the foregoing discussion,relevant knowledge in the art and references discussed above inconnection with the Background, the disclosures of which are allincorporated herein by reference, further description is deemedunnecessary. In addition, it should be understood from the foregoingdiscussion that aspects of the disclosure and portions of variousembodiments may be combined or interchanged either in whole or in part.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the disclosure. Finally, all patents, publications, andapplications referenced herein are incorporated by reference in theirentireties.

What is claimed is:
 1. A method for tuning characteristics of apolyamide nanofiber nonwoven comprising the steps of: targeting aspecific average nanofiber diameter and/or a specific relative viscosityfor the polyamide nanofiber nonwoven, wherein the specific averagenanofiber diameter is within a range from 100 nm to 1000 nm and/or thespecific relative viscosity is within a range from 5 to 75; extruding apolyamide composition having a moisture content with a pressurized gasthrough a fiber forming channel having a channel temperature to form thepolyamide nanofiber nonwoven having the target average nanofiberdiameter and/or relative viscosity; and controlling the moisture contentby drying the polyamide composition to have a moisture content of lessthan 0.02 wt. %, and rehydrating the dried polyamide composition.
 2. Themethod of claim 1, wherein the specific average nanofiber diameter iswithin a range of 200 nm to 700 nm.
 3. The method of claim 1, whereinthe specific relative viscosity is within a range from 15 to
 50. 4. Themethod of claim 1, wherein the moisture content is controlled from 0.005wt. % to 1 wt. %.
 5. The method of claim 1, wherein the pressure of thepressurized gas is controlled to range from 160 kPa to 220 kPa.
 6. Themethod of claim 1, wherein the channel temperature is controlled torange from 270° C. to 330° C.
 7. The method of claim 1, wherein thefiber forming channel comprises a die and/or a capillary.
 8. The methodof claim 1, wherein the polyamide nanofiber nonwoven is melt-blownand/or is free of solvent.
 9. The method of claim 1, wherein thepolyamide composition comprises a catalyst.
 10. A method for tuning therelative viscosity of a polyamide nanofiber nonwoven comprising thesteps of: targeting a specific relative viscosity for the polyamidenanofiber nonwoven, wherein the specific relative viscosity is within arange from 5 to 75; extruding a polyamide composition having a moisturecontent to form the polyamide nanofiber nonwoven having the targetrelative viscosity; and controlling the moisture content based on thetarget relative viscosity.
 11. The method of claim 10, wherein therelative viscosity is targeted to a targeted relative viscosity withinthe range from 15 to
 50. 12. The method of claim 10, wherein themoisture content is controlled to range from 0.005 wt. % to 1 wt. %. 13.The method of claim 10, wherein the moisture content is controlled torange from 0.02 wt. % to 0.3 wt. %.
 14. The method of claim 10, whereinthe controlling comprises: drying the polyamide composition to have amoisture content of less than 0.02 wt. %; and rehydrating the driedpolyamide composition.
 15. The method of claim 10, wherein the polyamidecomposition is extruded through a fiber forming channel having a channeltemperature and the channel temperature is controlled to range from 270°C. to 330° C.
 16. The method of claim 10, wherein the polyamidenanofiber nonwoven is melt-blown and/or is free of solvent.
 17. Themethod of claim 10, wherein the polyamide composition comprises acatalyst.
 18. The method of claim 1, wherein the polyamide nanofibernonwoven further comprises zinc oxide.
 19. The method of claim 10,wherein the polyamide nanofiber nonwoven further comprises zinc oxide.